Vulnerabilities > CVE-2020-5390 - Improper Verification of Cryptographic Signature vulnerability in multiple products

047910
CVSS 7.5 - HIGH
Attack vector
NETWORK
Attack complexity
LOW
Privileges required
NONE
Confidentiality impact
NONE
Integrity impact
HIGH
Availability impact
NONE
network
low complexity
pysaml2-project
canonical
debian
CWE-347
nessus

Summary

PySAML2 before 5.0.0 does not check that the signature in a SAML document is enveloped and thus signature wrapping is effective, i.e., it is affected by XML Signature Wrapping (XSW). The signature information and the node/object that is signed can be in different places and thus the signature verification will succeed, but the wrong data will be used. This specifically affects the verification of assertion that have been signed.

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-4630.NASL
    descriptionIt was discovered that pysaml2, a Python implementation of SAML to be used in a WSGI environment, was susceptible to XML signature wrapping attacks, which could result in a bypass of signature verification.
    last seen2020-03-17
    modified2020-02-24
    plugin id133878
    published2020-02-24
    reporterThis script is Copyright (C) 2020 and is owned by Tenable, Inc. or an Affiliate thereof.
    sourcehttps://www.tenable.com/plugins/nessus/133878
    titleDebian DSA-4630-1 : python-pysaml2 - security update
    code
    #
    # (C) Tenable Network Security, Inc.
    #
    # The descriptive text and package checks in this plugin were  
    # extracted from Debian Security Advisory DSA-4630. The text 
    # itself is copyright (C) Software in the Public Interest, Inc.
    #
    
    include("compat.inc");
    
    if (description)
    {
      script_id(133878);
      script_version("1.2");
      script_set_attribute(attribute:"plugin_modification_date", value:"2020/02/26");
    
      script_cve_id("CVE-2020-5390");
      script_xref(name:"DSA", value:"4630");
    
      script_name(english:"Debian DSA-4630-1 : python-pysaml2 - 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:
    "It was discovered that pysaml2, a Python implementation of SAML to be
    used in a WSGI environment, was susceptible to XML signature wrapping
    attacks, which could result in a bypass of signature verification."
      );
      # https://security-tracker.debian.org/tracker/source-package/python-pysaml2
      script_set_attribute(
        attribute:"see_also",
        value:"http://www.nessus.org/u?757b3296"
      );
      script_set_attribute(
        attribute:"see_also",
        value:"https://packages.debian.org/source/stretch/python-pysaml2"
      );
      script_set_attribute(
        attribute:"see_also",
        value:"https://packages.debian.org/source/buster/python-pysaml2"
      );
      script_set_attribute(
        attribute:"see_also",
        value:"https://www.debian.org/security/2020/dsa-4630"
      );
      script_set_attribute(
        attribute:"solution", 
        value:
    "Upgrade the python-pysaml2 packages.
    
    For the oldstable distribution (stretch), this problem has been fixed
    in version 3.0.0-5+deb9u1.
    
    For the stable distribution (buster), this problem has been fixed in
    version 5.4.1-2+deb10u1."
      );
      script_set_cvss_base_vector("CVSS2#AV:N/AC:L/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:L/PR:N/UI:N/S:U/C:N/I:H/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-pysaml2");
      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:"2020/01/13");
      script_set_attribute(attribute:"patch_publication_date", value:"2020/02/21");
      script_set_attribute(attribute:"plugin_publication_date", value:"2020/02/24");
      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:"10.0", prefix:"python-pysaml2", reference:"5.4.1-2+deb10u1")) flag++;
    if (deb_check(release:"10.0", prefix:"python-pysaml2-doc", reference:"5.4.1-2+deb10u1")) flag++;
    if (deb_check(release:"10.0", prefix:"python3-pysaml2", reference:"5.4.1-2+deb10u1")) flag++;
    if (deb_check(release:"9.0", prefix:"python-pysaml2", reference:"3.0.0-5+deb9u1")) flag++;
    if (deb_check(release:"9.0", prefix:"python-pysaml2-doc", reference:"3.0.0-5+deb9u1")) flag++;
    if (deb_check(release:"9.0", prefix:"python3-pysaml2", reference:"3.0.0-5+deb9u1")) flag++;
    
    if (flag)
    {
      if (report_verbosity > 0) security_warning(port:0, extra:deb_report_get());
      else security_warning(0);
      exit(0);
    }
    else audit(AUDIT_HOST_NOT, "affected");
    
  • NASL familyUbuntu Local Security Checks
    NASL idUBUNTU_USN-4245-1.NASL
    descriptionIt was discovered that PySAML2 incorrectly handled certain SAML files. An attacker could possibly use this issue to bypass signature verification with arbitrary data. 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 seen2020-06-01
    modified2020-06-02
    plugin id133179
    published2020-01-22
    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/133179
    titleUbuntu 16.04 LTS / 18.04 LTS / 19.04 / 19.10 : python-pysaml2 vulnerability (USN-4245-1)
  • NASL familyDebian Local Security Checks
    NASL idDEBIAN_DLA-2119.NASL
    descriptionIt was discovered that pysaml2, a Python implementation of SAML to be used in a WSGI environment, was susceptible to XML signature wrapping attacks, which could result in a bypass of signature verification. For Debian 8
    last seen2020-03-17
    modified2020-02-27
    plugin id134092
    published2020-02-27
    reporterThis script is Copyright (C) 2020 and is owned by Tenable, Inc. or an Affiliate thereof.
    sourcehttps://www.tenable.com/plugins/nessus/134092
    titleDebian DLA-2119-1 : python-pysaml2 security update