CVE-2020-5268: Sustainsys.Saml2 Subject Confirmation Method Not Validated Vulnerability

MODERATE
Advisory Identifier: GHSA-9475-xg6m-j7pw
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CVSS 6.5
CWE-303
Published
Advisory Summary

CVE-2020-5268 is a MODERATE (CVSS 6.5) subject confirmation method not validated vulnerability (CWE-303: Incorrect Implementation of Authentication Algorithm) affecting Sustainsys.Saml2 libraries in the NuGet ecosystem. The issue involves subject confirmation method not validated in saml2 authentication services for asp.net. Remediation is available by upgrading affected packages to version 1.0.2, 2.7.0.

CVE-2020-5268 at a Glance

CVE Identifier CVE-2020-5268
GHSA Identifier GHSA-9475-xg6m-j7pw
Severity MODERATE
CVSS v3.1 Base Score 6.5
CWE Classification CWE-303: Incorrect Implementation of Authentication Algorithm
Affected Product Sustainsys.Saml2
Package Ecosystem NuGet
Published Date
Last Updated

Security Impact

CVSS: 6.5

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:H/I:L/A:N).

Attack Vector Network (AV:N)
Attack Complexity High (AC:H)
Privileges Required Low (PR:L)
User Interaction Required (UI:R)
Scope Changed (S:C)
Confidentiality High (C:H)
Integrity Low (I:L)
Availability None (A:N)

How to Fix CVE-2020-5268

To remediate this vulnerability, upgrade all affected Sustainsys.Saml2 dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

Sustainsys.Saml2 fixed: 1.0.2 
Upgrade Sustainsys.Saml2 to 1.0.2
Sustainsys.Saml2 fixed: 2.7.0 
Upgrade Sustainsys.Saml2 to 2.7.0
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for Sustainsys.Saml2

How to Check if You Are Affected

To determine whether your application is affected by CVE-2020-5268, inspect your project dependencies for Sustainsys.Saml2:

inspect dependencies for Sustainsys.Saml2

Analyze the terminal output to locate any version of Sustainsys.Saml2 in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 1.0.2), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-303: Incorrect Implementation of Authentication Algorithm, where the requirements for the product dictate the use of an established authentication algorithm, but the implementation of the algorithm is incorrect. In Sustainsys.Saml2, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### Impact Saml2 tokens are usually used as bearer tokens - a caller that presents a token is assumed to be the subject of the token. There is also support in the Saml2 protocol for issuing tokens that is tied to a subject through other means, e.g. holder-of-key where possession of a private key must be proved. The Sustainsys.Saml2 library incorrectly treats all incoming tokens as bearer tokens, even though they have another subject confirmation method specified. This could be used by an attacker that could get access to Saml2 tokens with another subject confirmation method than bearer. The attacker could then use such a tocken to create a log in session. ### Patches Version 1.0.2 and 2.7.0 are patched. ### Workarounds Ensure that any IdentityProvider trusted by the Sustainsys.Saml2 SP only issues bearer tokens if the audience matches the Sustainsys.Saml2 SP. ### For more information If you have any questions or comments about this advisory: * Comment on #103 * Email us at security@sustainsys.com if you think that there are further security issues.

CVE-2020-5268 Affected Sustainsys.Saml2 Versions

2 component(s)
Fixed Versions:
1.0.22.7.0
Product / Package Ecosystem Affected Versions Fixed Version
Sustainsys.Saml2
nuget/Sustainsys.Saml2
NuGet
< 1.0.2
1.0.2
Sustainsys.Saml2
nuget/Sustainsys.Saml2
NuGet
≥ 2.0.0
< 2.7.0
2.7.0

References

GitHub Advisory / Wiki ADVISORY
https://github.com/Sustainsys/Saml2/security/advisories/GHSA-9475-xg6m-j7pw
NVD — CVE-2020-5268 NVD
https://nvd.nist.gov/vuln/detail/CVE-2020-5268
Sustainsys.Saml2 Source Repository REPOSITORY
https://github.com/Sustainsys/Saml2/issues/712
Security Fix Commit FIX COMMIT
https://github.com/Sustainsys/Saml2/commit/e58e0a1aff2b1ead6aca080b7cdced55ee6d5241
www.nuget.org/packages/sustainsys... WEB
https://www.nuget.org/packages/Sustainsys.Saml2

Frequently Asked Questions

What is CVE-2020-5268?
CVE-2020-5268 is a security vulnerability in Sustainsys.Saml2 involving Subject Confirmation Method not validated in Saml2 Authentication Services for ASP.NET under CWE-303: Incorrect Implementation of Authentication Algorithm.
Which Sustainsys.Saml2 versions are affected?
Affected versions include releases prior to 1.0.2, 2.7.0 across affected packages: Sustainsys.Saml2.
What version fixes CVE-2020-5268?
Upgrading to 1.0.2, 2.7.0 (or the latest patched release for your respective branch) resolves the vulnerability.
Is Sustainsys.Saml2 affected?
Yes, Sustainsys.Saml2 is affected in releases prior to 1.0.2, 2.7.0. Upgrade your dependency to 1.0.2, 2.7.0 or later.
What is the CVSS score of CVE-2020-5268?
CVE-2020-5268 has a CVSS v3.1 base score of 6.5 (MODERATE) with vector string CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:H/I:L/A:N.
What CWE is associated with CVE-2020-5268?
CVE-2020-5268 is classified under CWE-303: Incorrect Implementation of Authentication Algorithm (The requirements for the product dictate the use of an established authentication algorithm, but the implementation of the algorithm is incorrect.).
How can I check NuGet dependencies for CVE-2020-5268?
Run the dependency tree command: 'inspect dependencies for Sustainsys.Saml2'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-9475-xg6m-j7pw",
  "modified" : "2021-01-08T20:21:35Z",
  "published" : "2020-04-22T20:59:37Z",
  "aliases" : [ "CVE-2020-5268" ],
  "summary" : "Subject Confirmation Method not validated in Saml2 Authentication Services for ASP.NET",
  "details" : "### Impact\nSaml2 tokens are usually used as bearer tokens - a caller that presents a token is assumed to be the subject of the token. There is also support in the Saml2 protocol for issuing tokens that is tied to a subject through other means, e.g. holder-of-key where possession of a private key must be proved.\nThe Sustainsys.Saml2 library incorrectly treats all incoming tokens as bearer tokens, even though they have another subject confirmation method specified. This could be used by an attacker that could get access to Saml2 tokens with another subject confirmation method than bearer. The attacker could then use such a tocken to create a log in session.\n\n### Patches\nVersion 1.0.2 and 2.7.0 are patched.\n\n### Workarounds\nEnsure that any IdentityProvider trusted by the Sustainsys.Saml2 SP only issues bearer tokens if the audience matches the Sustainsys.Saml2 SP.\n\n### For more information\nIf you have any questions or comments about this advisory:\n* Comment on #103\n* Email us at security@sustainsys.com if you think that there are further security issues.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:H/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "NuGet",
      "name" : "Sustainsys.Saml2"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.0.2"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "NuGet",
      "name" : "Sustainsys.Saml2"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "2.0.0"
      }, {
        "fixed" : "2.7.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/Sustainsys/Saml2/security/advisories/GHSA-9475-xg6m-j7pw"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2020-5268"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/Sustainsys/Saml2/issues/712"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/Sustainsys/Saml2/commit/e58e0a1aff2b1ead6aca080b7cdced55ee6d5241"
  }, {
    "type" : "WEB",
    "url" : "https://www.nuget.org/packages/Sustainsys.Saml2"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-303" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2020-04-21T18:41:43Z",
    "nvd_published_at" : null
  }
}