Vulnerabilities > CVE-2011-0633 - Improper Input Validation vulnerability in multiple products

047910
CVSS 0.0 - NONE
Attack vector
UNKNOWN
Attack complexity
UNKNOWN
Privileges required
UNKNOWN
Confidentiality impact
UNKNOWN
Integrity impact
UNKNOWN
Availability impact
UNKNOWN

Summary

The Net::HTTPS module in libwww-perl (LWP) before 6.00, as used in WWW::Mechanize, LWP::UserAgent, and other products, when running in environments that do not set the If-SSL-Cert-Subject header, does not enable full validation of SSL certificates by default, which allows remote attackers to spoof servers via man-in-the-middle (MITM) attacks involving hostnames that are not properly validated. NOTE: it could be argued that this is a design limitation of the Net::HTTPS API, and separate implementations should be independently assigned CVE identifiers for not working around this limitation. However, because this API was modified within LWP, a single CVE identifier has been assigned.

Vulnerable Configurations

Part Description Count
Application
Search.Cpan
115
Application
Gisle_Aas
122

Common Weakness Enumeration (CWE)

Common Attack Pattern Enumeration and Classification (CAPEC)

  • Buffer Overflow via Environment Variables
    This attack pattern involves causing a buffer overflow through manipulation of environment variables. Once the attacker finds that they can modify an environment variable, they may try to overflow associated buffers. This attack leverages implicit trust often placed in environment variables.
  • Server Side Include (SSI) Injection
    An attacker can use Server Side Include (SSI) Injection to send code to a web application that then gets executed by the web server. Doing so enables the attacker to achieve similar results to Cross Site Scripting, viz., arbitrary code execution and information disclosure, albeit on a more limited scale, since the SSI directives are nowhere near as powerful as a full-fledged scripting language. Nonetheless, the attacker can conveniently gain access to sensitive files, such as password files, and execute shell commands.
  • Cross Zone Scripting
    An attacker is able to cause a victim to load content into their web-browser that bypasses security zone controls and gain access to increased privileges to execute scripting code or other web objects such as unsigned ActiveX controls or applets. This is a privilege elevation attack targeted at zone-based web-browser security. In a zone-based model, pages belong to one of a set of zones corresponding to the level of privilege assigned to that page. Pages in an untrusted zone would have a lesser level of access to the system and/or be restricted in the types of executable content it was allowed to invoke. In a cross-zone scripting attack, a page that should be assigned to a less privileged zone is granted the privileges of a more trusted zone. This can be accomplished by exploiting bugs in the browser, exploiting incorrect configuration in the zone controls, through a cross-site scripting attack that causes the attackers' content to be treated as coming from a more trusted page, or by leveraging some piece of system functionality that is accessible from both the trusted and less trusted zone. This attack differs from "Restful Privilege Escalation" in that the latter correlates to the inadequate securing of RESTful access methods (such as HTTP DELETE) on the server, while cross-zone scripting attacks the concept of security zones as implemented by a browser.
  • Cross Site Scripting through Log Files
    An attacker may leverage a system weakness where logs are susceptible to log injection to insert scripts into the system's logs. If these logs are later viewed by an administrator through a thin administrative interface and the log data is not properly HTML encoded before being written to the page, the attackers' scripts stored in the log will be executed in the administrative interface with potentially serious consequences. This attack pattern is really a combination of two other attack patterns: log injection and stored cross site scripting.
  • Command Line Execution through SQL Injection
    An attacker uses standard SQL injection methods to inject data into the command line for execution. This could be done directly through misuse of directives such as MSSQL_xp_cmdshell or indirectly through injection of data into the database that would be interpreted as shell commands. Sometime later, an unscrupulous backend application (or could be part of the functionality of the same application) fetches the injected data stored in the database and uses this data as command line arguments without performing proper validation. The malicious data escapes that data plane by spawning new commands to be executed on the host.

Nessus

  • NASL familySuSE Local Security Checks
    NASL idSUSE_11_4_PERL-LIBWWW-PERL-110526.NASL
    descriptionperl-libwww-perl did not verify enable host name checking of SSL certificates by default (CVE-2011-0633).
    last seen2020-06-01
    modified2020-06-02
    plugin id75995
    published2014-06-13
    reporterThis script is Copyright (C) 2014-2019 and is owned by Tenable, Inc. or an Affiliate thereof.
    sourcehttps://www.tenable.com/plugins/nessus/75995
    titleopenSUSE Security Update : perl-libwww-perl (openSUSE-SU-2011:0552-1)
    code
    #%NASL_MIN_LEVEL 80502
    #
    # (C) Tenable Network Security, Inc.
    #
    # The descriptive text and package checks in this plugin were
    # extracted from openSUSE Security Update perl-libwww-perl-4589.
    #
    # The text description of this plugin is (C) SUSE LLC.
    #
    
    include("compat.inc");
    
    if (description)
    {
      script_id(75995);
      script_version("1.4");
      script_cvs_date("Date: 2019/10/25 13:36:42");
    
      script_cve_id("CVE-2011-0633");
    
      script_name(english:"openSUSE Security Update : perl-libwww-perl (openSUSE-SU-2011:0552-1)");
      script_summary(english:"Check for the perl-libwww-perl-4589 patch");
    
      script_set_attribute(
        attribute:"synopsis", 
        value:"The remote openSUSE host is missing a security update."
      );
      script_set_attribute(
        attribute:"description", 
        value:
    "perl-libwww-perl did not verify enable host name checking of SSL
    certificates by default (CVE-2011-0633)."
      );
      script_set_attribute(
        attribute:"see_also",
        value:"https://bugzilla.novell.com/show_bug.cgi?id=693999"
      );
      script_set_attribute(
        attribute:"see_also",
        value:"https://lists.opensuse.org/opensuse-updates/2011-05/msg00058.html"
      );
      script_set_attribute(
        attribute:"solution", 
        value:"Update the affected perl-libwww-perl package."
      );
      script_set_cvss_base_vector("CVSS2#AV:N/AC:M/Au:N/C:N/I:P/A:N");
    
      script_set_attribute(attribute:"plugin_type", value:"local");
      script_set_attribute(attribute:"cpe", value:"p-cpe:/a:novell:opensuse:perl-libwww-perl");
      script_set_attribute(attribute:"cpe", value:"cpe:/o:novell:opensuse:11.4");
    
      script_set_attribute(attribute:"patch_publication_date", value:"2011/05/26");
      script_set_attribute(attribute:"plugin_publication_date", value:"2014/06/13");
      script_end_attributes();
    
      script_category(ACT_GATHER_INFO);
      script_copyright(english:"This script is Copyright (C) 2014-2019 and is owned by Tenable, Inc. or an Affiliate thereof.");
      script_family(english:"SuSE Local Security Checks");
    
      script_dependencies("ssh_get_info.nasl");
      script_require_keys("Host/local_checks_enabled", "Host/SuSE/release", "Host/SuSE/rpm-list");
    
      exit(0);
    }
    
    
    include("audit.inc");
    include("global_settings.inc");
    include("rpm.inc");
    
    if (!get_kb_item("Host/local_checks_enabled")) audit(AUDIT_LOCAL_CHECKS_NOT_ENABLED);
    release = get_kb_item("Host/SuSE/release");
    if (isnull(release) || release =~ "^(SLED|SLES)") audit(AUDIT_OS_NOT, "openSUSE");
    if (release !~ "^(SUSE11\.4)$") audit(AUDIT_OS_RELEASE_NOT, "openSUSE", "11.4", release);
    if (!get_kb_item("Host/SuSE/rpm-list")) audit(AUDIT_PACKAGE_LIST_MISSING);
    
    
    
    flag = 0;
    
    if ( rpm_check(release:"SUSE11.4", reference:"perl-libwww-perl-5.837-5.7.1") ) flag++;
    
    if (flag)
    {
      if (report_verbosity > 0) security_warning(port:0, extra:rpm_report_get());
      else security_warning(0);
      exit(0);
    }
    else
    {
      tested = pkg_tests_get();
      if (tested) audit(AUDIT_PACKAGE_NOT_AFFECTED, tested);
      else audit(AUDIT_PACKAGE_NOT_INSTALLED, "perl-libwww-perl");
    }
    
  • NASL familyGentoo Local Security Checks
    NASL idGENTOO_GLSA-201402-04.NASL
    descriptionThe remote host is affected by the vulnerability described in GLSA-201402-04 (libwww-perl: Multiple vulnerabilities) Multiple vulnerabilities have been discovered in libwww-perl. Please review the CVE identifiers referenced below for details. Impact : A remote attacker could entice a user to download a specially crafted file with an application linked against libwww-perl, which could result in overwritten files or arbitrary code execution by writing to a dotfile in the user’s home directory (such as .bashrc). Additionally, a remote attacker could perform a Man-in-the-Middle attack. Workaround : There is no known workaround at this time.
    last seen2020-06-01
    modified2020-06-02
    plugin id72314
    published2014-02-05
    reporterThis script is Copyright (C) 2014-2018 Tenable Network Security, Inc.
    sourcehttps://www.tenable.com/plugins/nessus/72314
    titleGLSA-201402-04 : libwww-perl: Multiple vulnerabilities
    code
    #
    # (C) Tenable Network Security, Inc.
    #
    # The descriptive text and package checks in this plugin were
    # extracted from Gentoo Linux Security Advisory GLSA 201402-04.
    #
    # The advisory text is Copyright (C) 2001-2015 Gentoo Foundation, Inc.
    # and licensed under the Creative Commons - Attribution / Share Alike 
    # license. See http://creativecommons.org/licenses/by-sa/3.0/
    #
    
    include("compat.inc");
    
    if (description)
    {
      script_id(72314);
      script_version("1.6");
      script_cvs_date("Date: 2018/07/12 19:01:15");
    
      script_cve_id("CVE-2010-2253", "CVE-2011-0633");
      script_bugtraq_id(47895);
      script_xref(name:"GLSA", value:"201402-04");
    
      script_name(english:"GLSA-201402-04 : libwww-perl: Multiple vulnerabilities");
      script_summary(english:"Checks for updated package(s) in /var/db/pkg");
    
      script_set_attribute(
        attribute:"synopsis", 
        value:
    "The remote Gentoo host is missing one or more security-related
    patches."
      );
      script_set_attribute(
        attribute:"description", 
        value:
    "The remote host is affected by the vulnerability described in GLSA-201402-04
    (libwww-perl: Multiple vulnerabilities)
    
        Multiple vulnerabilities have been discovered in libwww-perl. Please
          review the CVE identifiers referenced below for details.
      
    Impact :
    
        A remote attacker could entice a user to download a specially crafted
          file with an application linked against libwww-perl, which could result
          in overwritten files or arbitrary code execution by writing to a dotfile
          in the user’s home directory (such as .bashrc). Additionally, a remote
          attacker could perform a Man-in-the-Middle attack.
      
    Workaround :
    
        There is no known workaround at this time."
      );
      script_set_attribute(
        attribute:"see_also",
        value:"https://security.gentoo.org/glsa/201402-04"
      );
      script_set_attribute(
        attribute:"solution", 
        value:
    "All libwww-perl users should upgrade to the latest version:
          # emerge --sync
          # emerge --ask --oneshot --verbose '>=dev-perl/libwww-perl-6.30.0'
        NOTE: This is a legacy GLSA. Updates for all affected architectures are
          available since December 18, 2011. It is likely that your system is
          already no longer affected by this issue."
      );
      script_set_cvss_base_vector("CVSS2#AV:N/AC:M/Au:N/C:P/I:P/A:P");
      script_set_cvss_temporal_vector("CVSS2#E:U/RL:OF/RC:C");
      script_set_attribute(attribute:"exploitability_ease", value:"No known exploits are available");
      script_set_attribute(attribute:"exploit_available", value:"false");
    
      script_set_attribute(attribute:"plugin_type", value:"local");
      script_set_attribute(attribute:"cpe", value:"p-cpe:/a:gentoo:linux:libwww-perl");
      script_set_attribute(attribute:"cpe", value:"cpe:/o:gentoo:linux");
    
      script_set_attribute(attribute:"patch_publication_date", value:"2014/02/04");
      script_set_attribute(attribute:"plugin_publication_date", value:"2014/02/05");
      script_end_attributes();
    
      script_category(ACT_GATHER_INFO);
      script_copyright(english:"This script is Copyright (C) 2014-2018 Tenable Network Security, Inc.");
      script_family(english:"Gentoo Local Security Checks");
    
      script_dependencies("ssh_get_info.nasl");
      script_require_keys("Host/local_checks_enabled", "Host/Gentoo/release", "Host/Gentoo/qpkg-list");
    
      exit(0);
    }
    
    
    include("audit.inc");
    include("global_settings.inc");
    include("qpkg.inc");
    
    if (!get_kb_item("Host/local_checks_enabled")) audit(AUDIT_LOCAL_CHECKS_NOT_ENABLED);
    if (!get_kb_item("Host/Gentoo/release")) audit(AUDIT_OS_NOT, "Gentoo");
    if (!get_kb_item("Host/Gentoo/qpkg-list")) audit(AUDIT_PACKAGE_LIST_MISSING);
    
    
    flag = 0;
    
    if (qpkg_check(package:"dev-perl/libwww-perl", unaffected:make_list("ge 6.30.0"), vulnerable:make_list("lt 6.30.0"))) flag++;
    
    if (flag)
    {
      if (report_verbosity > 0) security_warning(port:0, extra:qpkg_report_get());
      else security_warning(0);
      exit(0);
    }
    else
    {
      tested = qpkg_tests_get();
      if (tested) audit(AUDIT_PACKAGE_NOT_AFFECTED, tested);
      else audit(AUDIT_PACKAGE_NOT_INSTALLED, "libwww-perl");
    }
    
  • NASL familySuSE Local Security Checks
    NASL idSUSE_11_PERL-LIBWWW-PERL-110523.NASL
    descriptionThis update fixes the issue that perl-libwww-perl does not enable host name verification of SSL certificates by default. This vulnerability could be exploited by a man in the middle attack. (CVE-2011-0633)
    last seen2020-06-01
    modified2020-06-02
    plugin id54920
    published2011-05-31
    reporterThis script is Copyright (C) 2011-2019 Tenable Network Security, Inc.
    sourcehttps://www.tenable.com/plugins/nessus/54920
    titleSuSE 11.1 Security Update : perl-libwww-perl (SAT Patch Number 4603)
    code
    #%NASL_MIN_LEVEL 80502
    #
    # (C) Tenable Network Security, Inc.
    #
    # The descriptive text and package checks in this plugin were  
    # extracted from SuSE 11 update information. The text itself is
    # copyright (C) Novell, Inc.
    #
    
    include("compat.inc");
    
    if (description)
    {
      script_id(54920);
      script_version("1.6");
      script_cvs_date("Date: 2019/10/25 13:36:43");
    
      script_cve_id("CVE-2011-0633");
    
      script_name(english:"SuSE 11.1 Security Update : perl-libwww-perl (SAT Patch Number 4603)");
      script_summary(english:"Checks rpm output for the updated package");
    
      script_set_attribute(
        attribute:"synopsis", 
        value:"The remote SuSE 11 host is missing a security update."
      );
      script_set_attribute(
        attribute:"description", 
        value:
    "This update fixes the issue that perl-libwww-perl does not enable host
    name verification of SSL certificates by default. This vulnerability
    could be exploited by a man in the middle attack. (CVE-2011-0633)"
      );
      script_set_attribute(
        attribute:"see_also",
        value:"https://bugzilla.novell.com/show_bug.cgi?id=693999"
      );
      script_set_attribute(
        attribute:"see_also",
        value:"http://support.novell.com/security/cve/CVE-2011-0633.html"
      );
      script_set_attribute(attribute:"solution", value:"Apply SAT patch number 4603.");
      script_set_cvss_base_vector("CVSS2#AV:N/AC:M/Au:N/C:N/I:P/A:N");
    
      script_set_attribute(attribute:"plugin_type", value:"local");
      script_set_attribute(attribute:"cpe", value:"p-cpe:/a:novell:suse_linux:11:perl-libwww-perl");
      script_set_attribute(attribute:"cpe", value:"cpe:/o:novell:suse_linux:11");
    
      script_set_attribute(attribute:"patch_publication_date", value:"2011/05/23");
      script_set_attribute(attribute:"plugin_publication_date", value:"2011/05/31");
      script_end_attributes();
    
      script_category(ACT_GATHER_INFO);
      script_copyright(english:"This script is Copyright (C) 2011-2019 Tenable Network Security, Inc.");
      script_family(english:"SuSE Local Security Checks");
    
      script_dependencies("ssh_get_info.nasl");
      script_require_keys("Host/local_checks_enabled", "Host/cpu", "Host/SuSE/release", "Host/SuSE/rpm-list");
    
      exit(0);
    }
    
    
    include("audit.inc");
    include("global_settings.inc");
    include("rpm.inc");
    
    
    if (!get_kb_item("Host/local_checks_enabled")) audit(AUDIT_LOCAL_CHECKS_NOT_ENABLED);
    release = get_kb_item("Host/SuSE/release");
    if (isnull(release) || release !~ "^(SLED|SLES)11") audit(AUDIT_OS_NOT, "SuSE 11");
    if (!get_kb_item("Host/SuSE/rpm-list")) audit(AUDIT_PACKAGE_LIST_MISSING);
    
    cpu = get_kb_item("Host/cpu");
    if (isnull(cpu)) audit(AUDIT_UNKNOWN_ARCH);
    if (cpu !~ "^i[3-6]86$" && "x86_64" >!< cpu && "s390x" >!< cpu) audit(AUDIT_LOCAL_CHECKS_NOT_IMPLEMENTED, "SuSE 11", cpu);
    
    pl = get_kb_item("Host/SuSE/patchlevel");
    if (isnull(pl) || int(pl) != 1) audit(AUDIT_OS_NOT, "SuSE 11.1");
    
    
    flag = 0;
    if (rpm_check(release:"SLED11", sp:1, cpu:"i586", reference:"perl-libwww-perl-5.816-2.17.1")) flag++;
    if (rpm_check(release:"SLED11", sp:1, cpu:"x86_64", reference:"perl-libwww-perl-5.816-2.17.1")) flag++;
    if (rpm_check(release:"SLES11", sp:1, reference:"perl-libwww-perl-5.816-2.17.1")) flag++;
    
    
    if (flag)
    {
      if (report_verbosity > 0) security_warning(port:0, extra:rpm_report_get());
      else security_warning(0);
      exit(0);
    }
    else audit(AUDIT_HOST_NOT, "affected");
    
  • NASL familyAmazon Linux Local Security Checks
    NASL idALA_ALAS-2011-17.NASL
    descriptionThe Net::HTTPS module in libwww-perl (LWP) before 6.00, as used in WWW::Mechanize, LWP::UserAgent, and other products, when running in environments that do not set the If-SSL-Cert-Subject header, does not enable full validation of SSL certificates by default, which allows remote attackers to spoof servers via man-in-the-middle (MITM) attacks involving hostnames that are not properly validated. NOTE: it could be argued that this is a design limitation of the Net::HTTPS API, and separate implementations should be independently assigned CVE identifiers for not working around this limitation. However, because this API was modified within LWP, a single CVE identifier has been assigned.
    last seen2020-06-01
    modified2020-06-02
    plugin id69576
    published2013-09-04
    reporterThis script is Copyright (C) 2013-2018 Tenable Network Security, Inc.
    sourcehttps://www.tenable.com/plugins/nessus/69576
    titleAmazon Linux AMI : perl-libwww-perl (ALAS-2011-17)
    code
    #
    # (C) Tenable Network Security, Inc.
    #
    # The descriptive text and package checks in this plugin were
    # extracted from Amazon Linux AMI Security Advisory ALAS-2011-17.
    #
    
    include("compat.inc");
    
    if (description)
    {
      script_id(69576);
      script_version("1.5");
      script_cvs_date("Date: 2018/04/18 15:09:34");
    
      script_cve_id("CVE-2011-0633");
      script_xref(name:"ALAS", value:"2011-17");
    
      script_name(english:"Amazon Linux AMI : perl-libwww-perl (ALAS-2011-17)");
      script_summary(english:"Checks rpm output for the updated package");
    
      script_set_attribute(
        attribute:"synopsis", 
        value:"The remote Amazon Linux AMI host is missing a security update."
      );
      script_set_attribute(
        attribute:"description", 
        value:
    "The Net::HTTPS module in libwww-perl (LWP) before 6.00, as used in
    WWW::Mechanize, LWP::UserAgent, and other products, when running in
    environments that do not set the If-SSL-Cert-Subject header, does not
    enable full validation of SSL certificates by default, which allows
    remote attackers to spoof servers via man-in-the-middle (MITM) attacks
    involving hostnames that are not properly validated. NOTE: it could be
    argued that this is a design limitation of the Net::HTTPS API, and
    separate implementations should be independently assigned CVE
    identifiers for not working around this limitation. However, because
    this API was modified within LWP, a single CVE identifier has been
    assigned."
      );
      script_set_attribute(
        attribute:"see_also",
        value:"https://alas.aws.amazon.com/ALAS-2011-17.html"
      );
      script_set_attribute(
        attribute:"solution", 
        value:"Run 'yum update perl-libwww-perl' to update your system."
      );
      script_set_cvss_base_vector("CVSS2#AV:N/AC:M/Au:N/C:N/I:P/A:N");
    
      script_set_attribute(attribute:"plugin_type", value:"local");
      script_set_attribute(attribute:"cpe", value:"p-cpe:/a:amazon:linux:perl-libwww-perl");
      script_set_attribute(attribute:"cpe", value:"cpe:/o:amazon:linux");
    
      script_set_attribute(attribute:"patch_publication_date", value:"2011/10/31");
      script_set_attribute(attribute:"plugin_publication_date", value:"2013/09/04");
      script_end_attributes();
    
      script_category(ACT_GATHER_INFO);
      script_copyright(english:"This script is Copyright (C) 2013-2018 Tenable Network Security, Inc.");
      script_family(english:"Amazon Linux Local Security Checks");
    
      script_dependencies("ssh_get_info.nasl");
      script_require_keys("Host/local_checks_enabled", "Host/AmazonLinux/release", "Host/AmazonLinux/rpm-list");
    
      exit(0);
    }
    
    
    include("audit.inc");
    include("global_settings.inc");
    include("rpm.inc");
    
    
    if (!get_kb_item("Host/local_checks_enabled")) audit(AUDIT_LOCAL_CHECKS_NOT_ENABLED);
    
    release = get_kb_item("Host/AmazonLinux/release");
    if (isnull(release) || !strlen(release)) audit(AUDIT_OS_NOT, "Amazon Linux");
    os_ver = pregmatch(pattern: "^AL(A|\d)", string:release);
    if (isnull(os_ver)) audit(AUDIT_UNKNOWN_APP_VER, "Amazon Linux");
    os_ver = os_ver[1];
    if (os_ver != "A")
    {
      if (os_ver == 'A') os_ver = 'AMI';
      audit(AUDIT_OS_NOT, "Amazon Linux AMI", "Amazon Linux " + os_ver);
    }
    
    if (!get_kb_item("Host/AmazonLinux/rpm-list")) audit(AUDIT_PACKAGE_LIST_MISSING);
    
    
    flag = 0;
    if (rpm_check(release:"ALA", reference:"perl-libwww-perl-5.837-4.1.amzn1")) flag++;
    
    if (flag)
    {
      if (report_verbosity > 0) security_warning(port:0, extra:rpm_report_get());
      else security_warning(0);
      exit(0);
    }
    else
    {
      tested = pkg_tests_get();
      if (tested) audit(AUDIT_PACKAGE_NOT_AFFECTED, tested);
      else audit(AUDIT_PACKAGE_NOT_INSTALLED, "perl-libwww-perl");
    }
    

Seebug

bulletinFamilyexploit
descriptionBUGTRAQ ID: 47895 CVE ID: CVE-2011-0633 CPAN(Comprehensive Perl Archive Network)中译为“Perl综合典藏网”,“Perl综合档案网”或者“Perl程序库”。它包含了极多用Perl写成的软件和其文件。 Perl libwww-perl (LWP)模块在SSL证书验证上存在安全策略绕过漏洞,远程攻击者可利用此漏洞执行中间人攻击或伪造受信任服务器。 libwww-perl (LWP) 6.00之前版本中的Net::HTTPS模块(也使用在其他产品中,如WWW::Mechanize, LWP::UserAgent)在没有设置If-SSL-Cert-Subject标头的环境下运行时,默认没有启用对SSL证书的完整验证,可使远程攻击者通过没有正确验证主机名的中间人攻击伪造服务器。 CPAN libwww-perl 5.837 厂商补丁: CPAN ---- 目前厂商已经发布了升级补丁以修复这个安全问题,请到厂商的主页下载: http://www.cpan.org
idSSV:20572
last seen2017-11-19
modified2011-05-20
published2011-05-20
reporterRoot
titlePerl libwww-perl (LWP)模块SSL证书验证安全策略绕过漏洞