CVE-2021-31805: Struts2 core Expression Language Injection Vulnerability

CRITICAL
Advisory Identifier: GHSA-v8j6-6c2r-r27c
Share
CVSS 9.8
CWE-917
Published
Advisory Summary

CVE-2021-31805 is a CRITICAL (CVSS 9.8) expression language injection vulnerability (CWE-917: Improper Neutralization of Special Elements used in an Expression Language Statement ('Expression Language Injection')) affecting Struts2 core libraries in the Maven ecosystem. The issue involves expression language injection in apache struts. Remediation is available by upgrading affected packages to version 2.5.30.

CVE-2021-31805 at a Glance

CVE Identifier CVE-2021-31805
GHSA Identifier GHSA-v8j6-6c2r-r27c
Severity CRITICAL
CVSS v3.1 Base Score 9.8
CWE Classification CWE-917: Improper Neutralization of Special Elements used in an Expression Language Statement ('Expression Language Injection')
Affected Product Struts2 core
Package Ecosystem Maven
Published Date
Last Updated

Security Impact

CVSS: 9.8

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

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
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-2021-31805

To remediate this vulnerability, upgrade all affected Struts2 core 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.apache.struts:struts2-core fixed: 2.5.30 
<dependency>
    <groupId>org.apache.struts</groupId>
    <artifactId>struts2-core</artifactId>
    <version>2.5.30</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.apache.struts

How to Check if You Are Affected

To determine whether your Java application is affected by CVE-2021-31805, inspect your build dependencies using the Maven Dependency Plugin:

mvn dependency:tree -Dincludes=org.apache.struts

Analyze the terminal output to locate any version of Struts2 core in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 2.5.30), your application is affected.

Note: The mvn dependency:tree -Dincludes=org.apache.struts 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-917: Improper Neutralization of Special Elements used in an Expression Language Statement ('Expression Language Injection'), where the product constructs all or part of an expression language (el) statement in a framework such as a java server page (jsp) using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended el statement before it is executed. In Struts2 core, 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

The fix issued for CVE-2020-17530 was incomplete. So from Apache Struts 2.0.0 to 2.5.29, still some of the tag’s attributes could perform a double evaluation if a developer applied forced OGNL evaluation by using the %{...} syntax. Using forced OGNL evaluation on untrusted user input can lead to a Remote Code Execution and security degradation.

CVE-2021-31805 Affected Struts2 core Versions

1 component(s)
Fixed Versions:
2.5.30
Product / Package Ecosystem Affected Versions Fixed Version
org.apache.struts:struts2-core
maven/org.apache.struts/struts2-core
Maven
≥ 2.0.0
< 2.5.30
2.5.30

References

NVD — CVE-2021-31805 NVD
https://nvd.nist.gov/vuln/detail/CVE-2021-31805
cwiki.apache.org/confluence/display/... WEB
https://cwiki.apache.org/confluence/display/WW/S2-062
Struts2 core Security Information SECURITY
https://security.netapp.com/advisory/ntap-20220420-0001
Struts2 core Security Information SECURITY
https://www.oracle.com/security-alerts/cpujul2022.html
Struts2 core Security Information SECURITY
http://www.openwall.com/lists/oss-security/2022/04/12/6

Frequently Asked Questions

What is CVE-2021-31805?
CVE-2021-31805 is a security vulnerability in Struts2 core involving Expression Language Injection in Apache Struts under CWE-917: Improper Neutralization of Special Elements used in an Expression Language Statement ('Expression Language Injection').
Which Struts2 core versions are affected?
Affected versions include releases prior to 2.5.30 across affected packages: org.apache.struts:struts2-core.
What version fixes CVE-2021-31805?
Upgrading to 2.5.30 (or the latest patched release for your respective branch) resolves the vulnerability.
Is struts2-core affected?
Yes, org.apache.struts:struts2-core is affected in releases prior to 2.5.30. Upgrade your dependency to 2.5.30 or later.
What is the CVSS score of CVE-2021-31805?
CVE-2021-31805 has a CVSS v3.1 base score of 9.8 (CRITICAL) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.
What CWE is associated with CVE-2021-31805?
CVE-2021-31805 is classified under CWE-917: Improper Neutralization of Special Elements used in an Expression Language Statement ('Expression Language Injection') (The product constructs all or part of an expression language (EL) statement in a framework such as a Java Server Page (JSP) using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended EL statement before it is executed.).
How can I check Maven dependencies for CVE-2021-31805?
Run the dependency tree command: 'mvn dependency:tree -Dincludes=org.apache.struts'. 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-v8j6-6c2r-r27c",
  "modified" : "2022-07-27T04:19:48Z",
  "published" : "2022-04-13T00:00:30Z",
  "aliases" : [ "CVE-2021-31805" ],
  "summary" : "Expression Language Injection in Apache Struts",
  "details" : "The fix issued for CVE-2020-17530 was incomplete. So from Apache Struts 2.0.0 to 2.5.29, still some of the tag’s attributes could perform a double evaluation if a developer applied forced OGNL evaluation by using the %{...} syntax. Using forced OGNL evaluation on untrusted user input can lead to a Remote Code Execution and security degradation.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.apache.struts:struts2-core"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "2.0.0"
      }, {
        "fixed" : "2.5.30"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2021-31805"
  }, {
    "type" : "WEB",
    "url" : "https://cwiki.apache.org/confluence/display/WW/S2-062"
  }, {
    "type" : "WEB",
    "url" : "https://security.netapp.com/advisory/ntap-20220420-0001"
  }, {
    "type" : "WEB",
    "url" : "https://www.oracle.com/security-alerts/cpujul2022.html"
  }, {
    "type" : "WEB",
    "url" : "http://www.openwall.com/lists/oss-security/2022/04/12/6"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-917" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2022-04-22T20:30:35Z",
    "nvd_published_at" : "2022-04-12T16:15:00Z"
  }
}