Vulnerabilities > CVE-2019-15796 - Improper Verification of Cryptographic Signature vulnerability in multiple products

047910
CVSS 2.6 - LOW
Attack vector
NETWORK
Attack complexity
HIGH
Privileges required
NONE
Confidentiality impact
NONE
Integrity impact
PARTIAL
Availability impact
NONE
network
high complexity
ubuntu
canonical
debian
CWE-347
nessus
NVD
Published: 2020-03-26
Updated: 2020-10-19

Summary

Python-apt doesn't check if hashes are signed in `Version.fetch_binary()` and `Version.fetch_source()` of apt/package.py or in `_fetch_archives()` of apt/cache.py in version 1.9.3ubuntu2 and earlier. This allows downloads from unsigned repositories which shouldn't be allowed and has been fixed in verisions 1.9.5, 1.9.0ubuntu1.2, 1.6.5ubuntu0.1, 1.1.0~beta1ubuntu0.16.04.7, 0.9.3.5ubuntu3+esm2, and 0.8.3ubuntu7.5.

Vulnerable Configurations

Part Description Count
Application
Ubuntu
65
Application
Debian
1
OS
Canonical
6

Common Weakness Enumeration (CWE)

Common Attack Pattern Enumeration and Classification (CAPEC)

  • Padding Oracle Crypto Attack
    An attacker is able to efficiently decrypt data without knowing the decryption key if a target system leaks data on whether or not a padding error happened while decrypting the ciphertext. A target system that leaks this type of information becomes the padding oracle and an attacker is able to make use of that oracle to efficiently decrypt data without knowing the decryption key by issuing on average 128*b calls to the padding oracle (where b is the number of bytes in the ciphertext block). In addition to performing decryption, an attacker is also able to produce valid ciphertexts (i.e., perform encryption) by using the padding oracle, all without knowing the encryption key. Any cryptosystem can be vulnerable to padding oracle attacks if the encrypted messages are not authenticated to ensure their validity prior to decryption, and then the information about padding error is leaked to the attacker. This attack technique may be used, for instance, to break CAPTCHA systems or decrypt/modify state information stored in client side objects (e.g., hidden fields or cookies). This attack technique is a side-channel attack on the cryptosystem that uses a data leak from an improperly implemented decryption routine to completely subvert the cryptosystem. The one bit of information that tells the attacker whether a padding error during decryption has occurred, in whatever form it comes, is sufficient for the attacker to break the cryptosystem. That bit of information can come in a form of an explicit error message about a padding error, a returned blank page, or even the server taking longer to respond (a timing attack). This attack can be launched cross domain where an attacker is able to use cross-domain information leaks to get the bits of information from the padding oracle from a target system / service with which the victim is communicating. To do so an attacker sends a request containing ciphertext to the target system. Due to the browser's same origin policy, the attacker is not able to see the response directly, but can use cross-domain information leak techniques to still get the information needed (i.e., information on whether or not a padding error has occurred). For instance, this can be done using "img" tag plus the onerror()/onload() events. The attacker's JavaScript can make web browsers to load an image on the target site, and know if the image is loaded or not. This is 1-bit information needed for the padding oracle attack to work: if the image is loaded, then it is valid padding, otherwise it is not.

Nessus

  • NASL familyDebian Local Security Checks
    NASL idDEBIAN_DSA-4609.NASL
    descriptionTwo security issues were found in the Python interface to the apt package manager; package downloads from unsigned repositories were incorrectly rejected and the hash validation relied on MD5.
    last seen2020-04-16
    modified2020-01-27
    plugin id133230
    published2020-01-27
    reporterThis script is Copyright (C) 2020 and is owned by Tenable, Inc. or an Affiliate thereof.
    sourcehttps://www.tenable.com/plugins/nessus/133230
    titleDebian DSA-4609-1 : python-apt - security update
    code
    #
# (C) Tenable Network Security, Inc.
#
# The descriptive text and package checks in this plugin were  
# extracted from Debian Security Advisory DSA-4609. The text 
# itself is copyright (C) Software in the Public Interest, Inc.
#

include("compat.inc");

if (description)
{
  script_id(133230);
  script_version("1.4");
  script_set_attribute(attribute:"plugin_modification_date", value:"2020/04/14");

  script_cve_id("CVE-2019-15795", "CVE-2019-15796");
  script_xref(name:"DSA", value:"4609");

  script_name(english:"Debian DSA-4609-1 : python-apt - security update");
  script_summary(english:"Checks dpkg output for the updated package");

  script_set_attribute(
    attribute:"synopsis", 
    value:"The remote Debian host is missing a security-related update."
  );
  script_set_attribute(
    attribute:"description", 
    value:
"Two security issues were found in the Python interface to the apt
package manager; package downloads from unsigned repositories were
incorrectly rejected and the hash validation relied on MD5."
  );
  script_set_attribute(
    attribute:"see_also",
    value:"https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=944696"
  );
  script_set_attribute(
    attribute:"see_also",
    value:"https://security-tracker.debian.org/tracker/source-package/python-apt"
  );
  script_set_attribute(
    attribute:"see_also",
    value:"https://packages.debian.org/source/stretch/python-apt"
  );
  script_set_attribute(
    attribute:"see_also",
    value:"https://packages.debian.org/source/buster/python-apt"
  );
  script_set_attribute(
    attribute:"see_also",
    value:"https://www.debian.org/security/2020/dsa-4609"
  );
  script_set_attribute(
    attribute:"solution", 
    value:
"Upgrade the python-apt packages.

For the oldstable distribution (stretch), these problems have been
fixed in version 1.4.1.

For the stable distribution (buster), these problems have been fixed
in version 1.8.4.1."
  );
  script_set_cvss_base_vector("CVSS2#AV:N/AC:H/Au:N/C:N/I:P/A:N");
  script_set_cvss_temporal_vector("CVSS2#E:U/RL:OF/RC:C");
  script_set_cvss3_base_vector("CVSS:3.0/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:L/A:N");
  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:debian:debian_linux:python-apt");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:debian:debian_linux:10.0");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:debian:debian_linux:9.0");

  script_set_attribute(attribute:"vuln_publication_date", value:"2020/03/26");
  script_set_attribute(attribute:"patch_publication_date", value:"2020/01/23");
  script_set_attribute(attribute:"plugin_publication_date", value:"2020/01/27");
  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:"Debian Local Security Checks");

  script_dependencies("ssh_get_info.nasl");
  script_require_keys("Host/local_checks_enabled", "Host/Debian/release", "Host/Debian/dpkg-l");

  exit(0);
}


include("audit.inc");
include("debian_package.inc");


if (!get_kb_item("Host/local_checks_enabled")) audit(AUDIT_LOCAL_CHECKS_NOT_ENABLED);
if (!get_kb_item("Host/Debian/release")) audit(AUDIT_OS_NOT, "Debian");
if (!get_kb_item("Host/Debian/dpkg-l")) audit(AUDIT_PACKAGE_LIST_MISSING);


flag = 0;
if (deb_check(release:"10.0", prefix:"python-apt", reference:"1.8.4.1")) flag++;
if (deb_check(release:"10.0", prefix:"python-apt-common", reference:"1.8.4.1")) flag++;
if (deb_check(release:"10.0", prefix:"python-apt-dbg", reference:"1.8.4.1")) flag++;
if (deb_check(release:"10.0", prefix:"python-apt-dev", reference:"1.8.4.1")) flag++;
if (deb_check(release:"10.0", prefix:"python-apt-doc", reference:"1.8.4.1")) flag++;
if (deb_check(release:"10.0", prefix:"python3-apt", reference:"1.8.4.1")) flag++;
if (deb_check(release:"10.0", prefix:"python3-apt-dbg", reference:"1.8.4.1")) flag++;
if (deb_check(release:"9.0", prefix:"python-apt", reference:"1.4.1")) flag++;
if (deb_check(release:"9.0", prefix:"python-apt-common", reference:"1.4.1")) flag++;
if (deb_check(release:"9.0", prefix:"python-apt-dbg", reference:"1.4.1")) flag++;
if (deb_check(release:"9.0", prefix:"python-apt-dev", reference:"1.4.1")) flag++;
if (deb_check(release:"9.0", prefix:"python-apt-doc", reference:"1.4.1")) flag++;
if (deb_check(release:"9.0", prefix:"python3-apt", reference:"1.4.1")) flag++;
if (deb_check(release:"9.0", prefix:"python3-apt-dbg", reference:"1.4.1")) flag++;

if (flag)
{
  if (report_verbosity > 0) security_note(port:0, extra:deb_report_get());
  else security_note(0);
  exit(0);
}
else audit(AUDIT_HOST_NOT, "affected");
  • NASL familyDebian Local Security Checks
    NASL idDEBIAN_DLA-2074.NASL
    descriptionSeveral issues have been found in python-apt, a python interface to libapt-pkg. CVE-2019-15795 It was discovered that python-apt would still use MD5 hashes to validate certain downloaded packages. If a remote attacker were able to perform a man-in-the-middle attack, this flaw could potentially be used to install altered packages. CVE-2019-15796 It was discovered that python-apt could install packages from untrusted repositories, contrary to expectations. For Debian 8
    last seen2020-04-16
    modified2020-01-24
    plugin id133219
    published2020-01-24
    reporterThis script is Copyright (C) 2020 and is owned by Tenable, Inc. or an Affiliate thereof.
    sourcehttps://www.tenable.com/plugins/nessus/133219
    titleDebian DLA-2074-1 : python-apt security update
    code
    #
# (C) Tenable Network Security, Inc.
#
# The descriptive text and package checks in this plugin were
# extracted from Debian Security Advisory DLA-2074-1. The text
# itself is copyright (C) Software in the Public Interest, Inc.
#

include("compat.inc");

if (description)
{
  script_id(133219);
  script_version("1.4");
  script_set_attribute(attribute:"plugin_modification_date", value:"2020/04/14");

  script_cve_id("CVE-2019-15795", "CVE-2019-15796");

  script_name(english:"Debian DLA-2074-1 : python-apt security update");
  script_summary(english:"Checks dpkg output for the updated packages.");

  script_set_attribute(
    attribute:"synopsis", 
    value:"The remote Debian host is missing a security update."
  );
  script_set_attribute(
    attribute:"description", 
    value:
"Several issues have been found in python-apt, a python interface to
libapt-pkg.

CVE-2019-15795

It was discovered that python-apt would still use MD5 hashes to
validate certain downloaded packages. If a remote attacker were able
to perform a man-in-the-middle attack, this flaw could potentially be
used to install altered packages.

CVE-2019-15796

It was discovered that python-apt could install packages from
untrusted repositories, contrary to expectations.

For Debian 8 'Jessie', these problems have been fixed in version
0.9.3.13.

We recommend that you upgrade your python-apt packages.

NOTE: Tenable Network Security has extracted the preceding description
block directly from the DLA security advisory. 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://lists.debian.org/debian-lts-announce/2020/01/msg00020.html"
  );
  script_set_attribute(
    attribute:"see_also",
    value:"https://packages.debian.org/source/jessie/python-apt"
  );
  script_set_attribute(attribute:"solution", value:"Upgrade the affected packages.");
  script_set_cvss_base_vector("CVSS2#AV:N/AC:H/Au:N/C:N/I:P/A:N");
  script_set_cvss_temporal_vector("CVSS2#E:U/RL:OF/RC:C");
  script_set_cvss3_base_vector("CVSS:3.0/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:L/A:N");
  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:debian:debian_linux:python-apt");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:debian:debian_linux:python-apt-common");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:debian:debian_linux:python-apt-dbg");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:debian:debian_linux:python-apt-dev");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:debian:debian_linux:python-apt-doc");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:debian:debian_linux:python3-apt");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:debian:debian_linux:python3-apt-dbg");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:debian:debian_linux:8.0");

  script_set_attribute(attribute:"vuln_publication_date", value:"2020/03/26");
  script_set_attribute(attribute:"patch_publication_date", value:"2020/01/23");
  script_set_attribute(attribute:"plugin_publication_date", value:"2020/01/24");
  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:"Debian Local Security Checks");

  script_dependencies("ssh_get_info.nasl");
  script_require_keys("Host/local_checks_enabled", "Host/Debian/release", "Host/Debian/dpkg-l");

  exit(0);
}


include("audit.inc");
include("debian_package.inc");


if (!get_kb_item("Host/local_checks_enabled")) audit(AUDIT_LOCAL_CHECKS_NOT_ENABLED);
if (!get_kb_item("Host/Debian/release")) audit(AUDIT_OS_NOT, "Debian");
if (!get_kb_item("Host/Debian/dpkg-l")) audit(AUDIT_PACKAGE_LIST_MISSING);


flag = 0;
if (deb_check(release:"8.0", prefix:"python-apt", reference:"0.9.3.13")) flag++;
if (deb_check(release:"8.0", prefix:"python-apt-common", reference:"0.9.3.13")) flag++;
if (deb_check(release:"8.0", prefix:"python-apt-dbg", reference:"0.9.3.13")) flag++;
if (deb_check(release:"8.0", prefix:"python-apt-dev", reference:"0.9.3.13")) flag++;
if (deb_check(release:"8.0", prefix:"python-apt-doc", reference:"0.9.3.13")) flag++;
if (deb_check(release:"8.0", prefix:"python3-apt", reference:"0.9.3.13")) flag++;
if (deb_check(release:"8.0", prefix:"python3-apt-dbg", reference:"0.9.3.13")) flag++;

if (flag)
{
  if (report_verbosity > 0) security_note(port:0, extra:deb_report_get());
  else security_note(0);
  exit(0);
}
else audit(AUDIT_HOST_NOT, "affected");
  • NASL familyUbuntu Local Security Checks
    NASL idUBUNTU_USN-4247-1.NASL
    descriptionIt was discovered that python-apt would still use MD5 hashes to validate certain downloaded packages. If a remote attacker were able to perform a man-in-the-middle attack, this flaw could potentially be used to install altered packages. (CVE-2019-15795) It was discovered that python-apt could install packages from untrusted repositories, contrary to expectations. (CVE-2019-15796). Note that Tenable Network Security has extracted the preceding description block directly from the Ubuntu security advisory. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.
    last seen2020-04-16
    modified2020-01-23
    plugin id133205
    published2020-01-23
    reporterUbuntu Security Notice (C) 2020 Canonical, Inc. / NASL script (C) 2020 and is owned by Tenable, Inc. or an Affiliate thereof.
    sourcehttps://www.tenable.com/plugins/nessus/133205
    titleUbuntu 16.04 LTS / 18.04 LTS / 19.04 / 19.10 : python-apt vulnerabilities (USN-4247-1)
  • NASL familyUbuntu Local Security Checks
    NASL idUBUNTU_USN-4247-2.NASL
    descriptionUSN-4247-1 fixed vulnerabilities in python-apt. The updated packages caused a regression when attempting to upgrade to a new Ubuntu release. This update fixes the problem. We apologize for the inconvenience. Original advisory details : It was discovered that python-apt would still use MD5 hashes to validate certain downloaded packages. If a remote attacker were able to perform a man-in-the-middle attack, this flaw could potentially be used to install altered packages. (CVE-2019-15795) It was discovered that python-apt could install packages from untrusted repositories, contrary to expectations. (CVE-2019-15796). Note that Tenable Network Security has extracted the preceding description block directly from the Ubuntu security advisory. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.
    last seen2020-04-16
    modified2020-01-23
    plugin id133206
    published2020-01-23
    reporterUbuntu Security Notice (C) 2020 Canonical, Inc. / NASL script (C) 2020 and is owned by Tenable, Inc. or an Affiliate thereof.
    sourcehttps://www.tenable.com/plugins/nessus/133206
    titleUbuntu 16.04 LTS / 18.04 LTS / 19.04 / 19.10 : python-apt regression (USN-4247-2)

References