CVE-2021-21657: Fstrigger XXE Vulnerability Vulnerability

HIGH
Advisory Identifier: GHSA-cphv-7cxw-5hcc
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CVSS 8.8
CWE-611
Published
Advisory Summary

CVE-2021-21657 is a HIGH (CVSS 8.8) xxe vulnerability vulnerability (CWE-611: Improper Restriction of XML External Entity Reference) affecting Fstrigger libraries in the Maven ecosystem. The issue involves xxe vulnerability in jenkins filesystem trigger plugin. Remediation is available by upgrading affected packages to version 0.41.

CVE-2021-21657 at a Glance

CVE Identifier CVE-2021-21657
GHSA Identifier GHSA-cphv-7cxw-5hcc
Severity HIGH
CVSS v3.1 Base Score 8.8
CWE Classification CWE-611: Improper Restriction of XML External Entity Reference
Affected Product Fstrigger
Package Ecosystem Maven
Published Date
Last Updated

Security Impact

CVSS: 8.8

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

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

How to Fix CVE-2021-21657

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

org.jenkins-ci.plugins:fstrigger fixed: 0.41 
<dependency>
    <groupId>org.jenkins-ci.plugins</groupId>
    <artifactId>fstrigger</artifactId>
    <version>0.41</version>
</dependency>
Verify Direct and Transitive Dependencies

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

mvn dependency:tree -Dincludes=org.jenkins-ci.plugins

How to Check if You Are Affected

To determine whether your Java application is affected by CVE-2021-21657, inspect your build dependencies using the Maven Dependency Plugin:

mvn dependency:tree -Dincludes=org.jenkins-ci.plugins

Analyze the terminal output to locate any version of Fstrigger in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 0.41), your application is affected.

Note: The mvn dependency:tree -Dincludes=org.jenkins-ci.plugins command inspects the resolved dependency graph declared in your project's POM files; it does not perform automated security scanning or inspect runtime dynamic classpaths. Always verify runtime container classpaths and shaded JARs.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-611: Improper Restriction of XML External Entity Reference, where the product processes an xml document that can contain xml entities with uris that resolve to documents outside of the intended sphere of control, causing the product to embed incorrect documents into its output. In Fstrigger, 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

Jenkins Filesystem Trigger Plugin 0.40 and earlier does not configure its XML parser to prevent XML external entity (XXE) attacks. This allows attackers with Job/Configure permission or otherwise able to control the contents of an XML file being polled for changes to have Jenkins parse a crafted XML document that uses external entities for extraction of secrets from the polling Jenkins controller or agent, server-side request forgery, or denial-of-service attacks. Jenkins Filesystem Trigger Plugin 0.41 disables external entity resolution for its XML parser.

CVE-2021-21657 Affected Fstrigger Versions

1 component(s)
Fixed Versions:
0.41
Product / Package Ecosystem Affected Versions Fixed Version
org.jenkins-ci.plugins:fstrigger
maven/org.jenkins-ci.plugins/fstrigger
Maven
< 0.41
0.41

References

NVD — CVE-2021-21657 NVD
https://nvd.nist.gov/vuln/detail/CVE-2021-21657
Fstrigger Source Repository REPOSITORY
https://github.com/jenkinsci/fstrigger-plugin
Fstrigger Security Information SECURITY
https://www.jenkins.io/security/advisory/2021-05-25/#SECURITY-2339
Fstrigger Security Information SECURITY
http://www.openwall.com/lists/oss-security/2021/05/25/3

Frequently Asked Questions

What is CVE-2021-21657?
CVE-2021-21657 is a security vulnerability in Fstrigger involving XXE vulnerability in Jenkins Filesystem Trigger Plugin under CWE-611: Improper Restriction of XML External Entity Reference.
Which Fstrigger versions are affected?
Affected versions include releases prior to 0.41 across affected packages: org.jenkins-ci.plugins:fstrigger.
What version fixes CVE-2021-21657?
Upgrading to 0.41 (or the latest patched release for your respective branch) resolves the vulnerability.
Is fstrigger affected?
Yes, org.jenkins-ci.plugins:fstrigger is affected in releases prior to 0.41. Upgrade your dependency to 0.41 or later.
What is the CVSS score of CVE-2021-21657?
CVE-2021-21657 has a CVSS v3.1 base score of 8.8 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H.
What CWE is associated with CVE-2021-21657?
CVE-2021-21657 is classified under CWE-611: Improper Restriction of XML External Entity Reference (The product processes an XML document that can contain XML entities with URIs that resolve to documents outside of the intended sphere of control, causing the product to embed incorrect documents into its output.).
How can I check Maven dependencies for CVE-2021-21657?
Run the dependency tree command: 'mvn dependency:tree -Dincludes=org.jenkins-ci.plugins'. 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-cphv-7cxw-5hcc",
  "modified" : "2023-10-27T14:56:59Z",
  "published" : "2022-05-24T19:03:11Z",
  "aliases" : [ "CVE-2021-21657" ],
  "summary" : "XXE vulnerability in Jenkins Filesystem Trigger Plugin",
  "details" : "Jenkins Filesystem Trigger Plugin 0.40 and earlier does not configure its XML parser to prevent XML external entity (XXE) attacks.\n\nThis allows attackers with Job/Configure permission or otherwise able to control the contents of an XML file being polled for changes to have Jenkins parse a crafted XML document that uses external entities for extraction of secrets from the polling Jenkins controller or agent, server-side request forgery, or denial-of-service attacks.\n\nJenkins Filesystem Trigger Plugin 0.41 disables external entity resolution for its XML parser.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.jenkins-ci.plugins:fstrigger"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.41"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.40"
    }
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2021-21657"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/jenkinsci/fstrigger-plugin"
  }, {
    "type" : "WEB",
    "url" : "https://www.jenkins.io/security/advisory/2021-05-25/#SECURITY-2339"
  }, {
    "type" : "WEB",
    "url" : "http://www.openwall.com/lists/oss-security/2021/05/25/3"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-611" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2022-12-15T17:35:15Z",
    "nvd_published_at" : "2021-05-25T17:15:00Z"
  }
}