CVE-2026-43971: Software Security Vulnerability Vulnerability

MODERATE
Advisory Identifier: GHSA-gg23-fwhr-prjh
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CWE-116
Published
Advisory Summary

CVE-2026-43971 is a MODERATE security vulnerability vulnerability (CWE-116: Improper Encoding or Escaping of Output) affecting Software libraries in the Maven ecosystem. The weakness occurs when the product prepares a structured message for communication with another component, but encoding or escaping of the data is either missing or done incorrectly. as a result, the intended structure of the message is not preserved.. Remediation is available in the latest vendor maintenance releases.

CVE-2026-43971 at a Glance

CVE Identifier CVE-2026-43971
GHSA Identifier GHSA-gg23-fwhr-prjh
Severity MODERATE
CVSS v3.1 Base Score N/A
CWE Classification CWE-116: Improper Encoding or Escaping of Output
Affected Product Software
Package Ecosystem Maven
Published Date
Last Updated

How to Fix CVE-2026-43971

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

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

How to Check if You Are Affected

To determine whether your Java application is affected by CVE-2026-43971, inspect your build dependencies using the Maven Dependency Plugin:

mvn dependency:tree

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

Note: The mvn dependency:tree 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-116: Improper Encoding or Escaping of Output, where the product prepares a structured message for communication with another component, but encoding or escaping of the data is either missing or done incorrectly. as a result, the intended structure of the message is not preserved. In Software, 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

Improper Encoding or Escaping of Output vulnerability in ninenines cowlib allows Link header directive smuggling via unescaped special characters in cow_link:link/1. cow_link:do_link/1 in cowlib interpolates the target URI, rel value, and attribute keys directly into the serialized Link: header value without escaping or token-grammar validation. A > byte in target prematurely closes the URI slot, allowing an attacker to append additional link entries with attacker-chosen rel directives. A " or \ in rel escapes the quoted string and opens new parameters. Any byte — including whitespace, =, and " — in an attribute key is emitted verbatim. Because browsers act on Link: directives such as rel="preconnect", rel="preload", and rel="prerender", an attacker who can influence these fields in an application that round-trips parsed Link headers through cow_link:link/1 can force victim browsers to make out-of-band connections to attacker-controlled origins. This issue affects cowlib: from 2.9.0 onward.

References

NVD — CVE-2026-43971 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-43971
Security Fix Commit FIX COMMIT
https://github.com/ninenines/cowlib/commit/485d58dfa91b91d98135dc95e5615f421715dae5
Security Fix Commit FIX COMMIT
https://github.com/ninenines/cowlib/commit/89da27ee4c241f5d649ba7d9b7f2188918af6cea
cna.erlef.org/cves/cve-2026-43971... WEB
https://cna.erlef.org/cves/CVE-2026-43971.html
osv.dev/vulnerability/eef-c... WEB
https://osv.dev/vulnerability/EEF-CVE-2026-43971

Frequently Asked Questions

What is CVE-2026-43971?
CVE-2026-43971 is a security vulnerability in Software classified as a security vulnerability vulnerability under CWE-116: Improper Encoding or Escaping of Output.
Which Software versions are affected?
Affected versions include releases prior to current release patches.
What version fixes CVE-2026-43971?
Upgrading to current release patches (or the latest patched release for your respective branch) resolves the vulnerability.
What CWE is associated with CVE-2026-43971?
CVE-2026-43971 is classified under CWE-116: Improper Encoding or Escaping of Output (The product prepares a structured message for communication with another component, but encoding or escaping of the data is either missing or done incorrectly. As a result, the intended structure of the message is not preserved.).
How can I check Maven dependencies for CVE-2026-43971?
Run the dependency tree command: 'mvn dependency:tree'. 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-gg23-fwhr-prjh",
  "modified" : "2026-09-16T21:31:36Z",
  "published" : "2026-08-18T09:30:27Z",
  "aliases" : [ "CVE-2026-43971" ],
  "details" : "Improper Encoding or Escaping of Output vulnerability in ninenines cowlib allows Link header directive smuggling via unescaped special characters in cow_link:link/1.\n\ncow_link:do_link/1 in cowlib interpolates the target URI, rel value, and attribute keys directly into the serialized Link: header value without escaping or token-grammar validation. A > byte in target prematurely closes the URI slot, allowing an attacker to append additional link entries with attacker-chosen rel directives. A \" or \\ in rel escapes the quoted string and opens new parameters. Any byte — including whitespace, =, and \" — in an attribute key is emitted verbatim. Because browsers act on Link: directives such as rel=\"preconnect\", rel=\"preload\", and rel=\"prerender\", an attacker who can influence these fields in an application that round-trips parsed Link headers through cow_link:link/1 can force victim browsers to make out-of-band connections to attacker-controlled origins.\n\nThis issue affects cowlib: from 2.9.0 onward.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X"
  } ],
  "affected" : [ ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-43971"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/ninenines/cowlib/commit/485d58dfa91b91d98135dc95e5615f421715dae5"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/ninenines/cowlib/commit/89da27ee4c241f5d649ba7d9b7f2188918af6cea"
  }, {
    "type" : "WEB",
    "url" : "https://cna.erlef.org/cves/CVE-2026-43971.html"
  }, {
    "type" : "WEB",
    "url" : "https://osv.dev/vulnerability/EEF-CVE-2026-43971"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-116" ],
    "severity" : "MODERATE",
    "github_reviewed" : false,
    "github_reviewed_at" : null,
    "nvd_published_at" : "2026-08-18T09:17:14Z"
  }
}