Vulnerabilities > CVE-2020-1747 - Improper Input Validation vulnerability in multiple products

047910
CVSS 9.8 - CRITICAL
Attack vector
NETWORK
Attack complexity
LOW
Privileges required
NONE
Confidentiality impact
HIGH
Integrity impact
HIGH
Availability impact
HIGH
network
low complexity
pyyaml
fedoraproject
opensuse
oracle
CWE-20
critical
nessus

Summary

A vulnerability was discovered in the PyYAML library in versions before 5.3.1, where it is susceptible to arbitrary code execution when it processes untrusted YAML files through the full_load method or with the FullLoader loader. Applications that use the library to process untrusted input may be vulnerable to this flaw. An attacker could use this flaw to execute arbitrary code on the system by abusing the python/object/new constructor.

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 familyFedora Local Security Checks
    NASL idFEDORA_2020-BDB0BFA928.NASL
    description - New upstream release 5.3.1 (rhbz#1814882) - Fixes CVE-2020-1747 (rhbz#1807367,1809011) Note that Tenable Network Security has extracted the preceding description block directly from the Fedora update system website. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.
    last seen2020-04-03
    modified2020-03-30
    plugin id134996
    published2020-03-30
    reporterThis script is Copyright (C) 2020 and is owned by Tenable, Inc. or an Affiliate thereof.
    sourcehttps://www.tenable.com/plugins/nessus/134996
    titleFedora 31 : PyYAML (2020-bdb0bfa928)
    code
    #
    # (C) Tenable Network Security, Inc.
    #
    # The descriptive text and package checks in this plugin were  
    # extracted from Fedora Security Advisory FEDORA-2020-bdb0bfa928.
    #
    
    include("compat.inc");
    
    if (description)
    {
      script_id(134996);
      script_version("1.3");
      script_set_attribute(attribute:"plugin_modification_date", value:"2020/04/02");
    
      script_cve_id("CVE-2020-1747");
      script_xref(name:"FEDORA", value:"2020-bdb0bfa928");
    
      script_name(english:"Fedora 31 : PyYAML (2020-bdb0bfa928)");
      script_summary(english:"Checks rpm output for the updated package.");
    
      script_set_attribute(
        attribute:"synopsis", 
        value:"The remote Fedora host is missing a security update."
      );
      script_set_attribute(
        attribute:"description", 
        value:
    "  - New upstream release 5.3.1 (rhbz#1814882)
    
      - Fixes CVE-2020-1747 (rhbz#1807367,1809011)
    
    Note that Tenable Network Security has extracted the preceding
    description block directly from the Fedora update system website.
    Tenable has attempted to automatically clean and format it as much as
    possible without introducing additional issues."
      );
      script_set_attribute(
        attribute:"see_also",
        value:"https://bodhi.fedoraproject.org/updates/FEDORA-2020-bdb0bfa928"
      );
      script_set_attribute(
        attribute:"solution", 
        value:"Update the affected PyYAML package."
      );
      script_set_cvss_base_vector("CVSS2#AV:N/AC:L/Au:N/C:C/I:C/A:C");
      script_set_cvss_temporal_vector("CVSS2#E:U/RL:OF/RC:C");
      script_set_cvss3_base_vector("CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H");
      script_set_cvss3_temporal_vector("CVSS:3.0/E:U/RL:O/RC:C");
      script_set_attribute(attribute:"exploitability_ease", value:"No known exploits are available");
    
      script_set_attribute(attribute:"plugin_type", value:"local");
      script_set_attribute(attribute:"cpe", value:"p-cpe:/a:fedoraproject:fedora:PyYAML");
      script_set_attribute(attribute:"cpe", value:"cpe:/o:fedoraproject:fedora:31");
    
      script_set_attribute(attribute:"vuln_publication_date", value:"2020/03/24");
      script_set_attribute(attribute:"patch_publication_date", value:"2020/03/27");
      script_set_attribute(attribute:"plugin_publication_date", value:"2020/03/30");
      script_set_attribute(attribute:"generated_plugin", value:"current");
      script_end_attributes();
    
      script_category(ACT_GATHER_INFO);
      script_copyright(english:"This script is Copyright (C) 2020 and is owned by Tenable, Inc. or an Affiliate thereof.");
      script_family(english:"Fedora Local Security Checks");
    
      script_dependencies("ssh_get_info.nasl");
      script_require_keys("Host/local_checks_enabled", "Host/RedHat/release", "Host/RedHat/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/RedHat/release");
    if (isnull(release) || "Fedora" >!< release) audit(AUDIT_OS_NOT, "Fedora");
    os_ver = pregmatch(pattern: "Fedora.*release ([0-9]+)", string:release);
    if (isnull(os_ver)) audit(AUDIT_UNKNOWN_APP_VER, "Fedora");
    os_ver = os_ver[1];
    if (! preg(pattern:"^31([^0-9]|$)", string:os_ver)) audit(AUDIT_OS_NOT, "Fedora 31", "Fedora " + os_ver);
    
    if (!get_kb_item("Host/RedHat/rpm-list")) audit(AUDIT_PACKAGE_LIST_MISSING);
    
    
    cpu = get_kb_item("Host/cpu");
    if (isnull(cpu)) audit(AUDIT_UNKNOWN_ARCH);
    if ("x86_64" >!< cpu && cpu !~ "^i[3-6]86$") audit(AUDIT_LOCAL_CHECKS_NOT_IMPLEMENTED, "Fedora", cpu);
    
    
    flag = 0;
    if (rpm_check(release:"FC31", reference:"PyYAML-5.3.1-1.fc31")) flag++;
    
    
    if (flag)
    {
      security_report_v4(
        port       : 0,
        severity   : SECURITY_HOLE,
        extra      : rpm_report_get()
      );
      exit(0);
    }
    else
    {
      tested = pkg_tests_get();
      if (tested) audit(AUDIT_PACKAGE_NOT_AFFECTED, tested);
      else audit(AUDIT_PACKAGE_NOT_INSTALLED, "PyYAML");
    }
    
  • NASL familyPhotonOS Local Security Checks
    NASL idPHOTONOS_PHSA-2020-1_0-0290_PYYAML.NASL
    descriptionAn update of the PyYAML package has been released.
    last seen2020-05-03
    modified2020-04-29
    plugin id136104
    published2020-04-29
    reporterThis script is Copyright (C) 2020 and is owned by Tenable, Inc. or an Affiliate thereof.
    sourcehttps://www.tenable.com/plugins/nessus/136104
    titlePhoton OS 1.0: Pyyaml PHSA-2020-1.0-0290
  • NASL familySuSE Local Security Checks
    NASL idSUSE_SU-2020-0959-1.NASL
    descriptionThis update for python-PyYAML fixes the following issues : CVE-2020-1747: Fixed an arbitrary code execution when YAML files are parsed by FullLoader (bsc#1165439). Note that Tenable Network Security has extracted the preceding description block directly from the SUSE security advisory. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.
    last seen2020-04-16
    modified2020-04-10
    plugin id135390
    published2020-04-10
    reporterThis script is Copyright (C) 2020 and is owned by Tenable, Inc. or an Affiliate thereof.
    sourcehttps://www.tenable.com/plugins/nessus/135390
    titleSUSE SLED15 / SLES15 Security Update : python-PyYAML (SUSE-SU-2020:0959-1)
  • NASL familySuSE Local Security Checks
    NASL idOPENSUSE-2020-630.NASL
    descriptionThis update for python-PyYAML fixes the following issues : - CVE-2020-1747: Fixed an arbitrary code execution when YAML files are parsed by FullLoader (bsc#1165439). This update was imported from the SUSE:SLE-15-SP1:Update update project.
    last seen2020-05-15
    modified2020-05-11
    plugin id136456
    published2020-05-11
    reporterThis script is Copyright (C) 2020 and is owned by Tenable, Inc. or an Affiliate thereof.
    sourcehttps://www.tenable.com/plugins/nessus/136456
    titleopenSUSE Security Update : python-PyYAML (openSUSE-2020-630)
  • NASL familySuSE Local Security Checks
    NASL idOPENSUSE-2020-507.NASL
    descriptionThis update for python-PyYAML fixes the following issues : - CVE-2020-1747: Fixed an arbitrary code execution when YAML files are parsed by FullLoader (bsc#1165439). This update was imported from the SUSE:SLE-15-SP1:Update update project.
    last seen2020-04-17
    modified2020-04-14
    plugin id135451
    published2020-04-14
    reporterThis script is Copyright (C) 2020 and is owned by Tenable, Inc. or an Affiliate thereof.
    sourcehttps://www.tenable.com/plugins/nessus/135451
    titleopenSUSE Security Update : python-PyYAML (openSUSE-2020-507)
  • NASL familyPhotonOS Local Security Checks
    NASL idPHOTONOS_PHSA-2020-3_0-0080_PYYAML.NASL
    descriptionAn update of the PyYAML package has been released.
    last seen2020-04-30
    modified2020-04-21
    plugin id135789
    published2020-04-21
    reporterThis script is Copyright (C) 2020 and is owned by Tenable, Inc. or an Affiliate thereof.
    sourcehttps://www.tenable.com/plugins/nessus/135789
    titlePhoton OS 3.0: Pyyaml PHSA-2020-3.0-0080
  • NASL familyFedora Local Security Checks
    NASL idFEDORA_2020-40C35D7B37.NASL
    description - New upstream release 5.3.1 (rhbz#1814882) - Fixes CVE-2020-1747 (rhbz#1807367,1809011) Note that Tenable Network Security has extracted the preceding description block directly from the Fedora update system website. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.
    last seen2020-04-03
    modified2020-03-30
    plugin id134991
    published2020-03-30
    reporterThis script is Copyright (C) 2020 and is owned by Tenable, Inc. or an Affiliate thereof.
    sourcehttps://www.tenable.com/plugins/nessus/134991
    titleFedora 30 : PyYAML (2020-40c35d7b37)
  • NASL familyFreeBSD Local Security Checks
    NASL idFREEBSD_PKG_AAE8FECF888E11EA971408002718DE91.NASL
    descriptionRiccardo Schirone (https://github.com/ret2libc) reports : In FullLoader python/object/new constructor, implemented by construct_python_object_apply, has support for setting the state of a deserialized instance through the set_python_instance_state method. After setting the state, some operations are performed on the instance to complete its initialization, however it is possible for an attacker to set the instance
    last seen2020-05-03
    modified2020-04-28
    plugin id136021
    published2020-04-28
    reporterThis script is Copyright (C) 2020 and is owned by Tenable, Inc. or an Affiliate thereof.
    sourcehttps://www.tenable.com/plugins/nessus/136021
    titleFreeBSD : py-yaml -- FullLoader (still) exploitable for arbitrary command execution (aae8fecf-888e-11ea-9714-08002718de91)
  • NASL familyPhotonOS Local Security Checks
    NASL idPHOTONOS_PHSA-2020-2_0-0229_PYYAML.NASL
    descriptionAn update of the PyYAML package has been released.
    last seen2020-04-30
    modified2020-04-22
    plugin id135866
    published2020-04-22
    reporterThis script is Copyright (C) 2020 and is owned by Tenable, Inc. or an Affiliate thereof.
    sourcehttps://www.tenable.com/plugins/nessus/135866
    titlePhoton OS 2.0: Pyyaml PHSA-2020-2.0-0229
  • NASL familySuSE Local Security Checks
    NASL idSUSE_SU-2020-1285-1.NASL
    descriptionThis update for python-PyYAML fixes the following issues : CVE-2020-1747: Fixed an arbitrary code execution when YAML files are parsed by FullLoader (bsc#1165439). Note that Tenable Network Security has extracted the preceding description block directly from the SUSE security advisory. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.
    last seen2020-05-31
    modified2020-05-22
    plugin id136784
    published2020-05-22
    reporterThis script is Copyright (C) 2020 and is owned by Tenable, Inc. or an Affiliate thereof.
    sourcehttps://www.tenable.com/plugins/nessus/136784
    titleSUSE SLES12 Security Update : python-PyYAML (SUSE-SU-2020:1285-1)