CVE-2026-43968: ninenines cowlib Improper Neutralization Of CRLF Sequences Vulnerability

MODERATE
Advisory Identifier: GHSA-hv23-4qp7-8c8r
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CVSS 4.0
CWE-93
Published
Advisory Summary

CVE-2026-43968 is a MODERATE (CVSS 4.0) improper neutralization of crlf sequences vulnerability (CWE-93: Improper Neutralization of CRLF Sequences ('CRLF Injection')) affecting ninenines cowlib libraries in the Hex ecosystem. The issue involves improper neutralization of crlf sequences ('crlf injection') vulnerability allows sse event splitting and injection via unvalidated field values. Remediation is available by upgrading affected packages to version 2.16.1.

CVE-2026-43968 at a Glance

CVE Identifier CVE-2026-43968
GHSA Identifier GHSA-hv23-4qp7-8c8r
Severity MODERATE
CVSS v3.1 Base Score 4.0
CWE Classification CWE-93: Improper Neutralization of CRLF Sequences ('CRLF Injection')
Affected Product ninenines cowlib
Package Ecosystem Hex
Published Date
Last Updated

Security Impact

CVSS: 4.0

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

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

How to Fix CVE-2026-43968

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

cowlib fixed: 2.16.1 
Upgrade cowlib to 2.16.1
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 cowlib

How to Check if You Are Affected

To determine whether your application is affected by CVE-2026-43968, inspect your project dependencies for ninenines cowlib:

inspect dependencies for cowlib

Analyze the terminal output to locate any version of ninenines cowlib in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 2.16.1), 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-93: Improper Neutralization of CRLF Sequences ('CRLF Injection'), where the product uses crlf (carriage return line feeds) as a special element, e.g. to separate lines or records, but it does not neutralize or incorrectly neutralizes crlf sequences from inputs. In ninenines cowlib, 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 Neutralization of CRLF Sequences ('CRLF Injection') vulnerability in ninenines cowlib allows SSE event splitting and injection via unvalidated field values. cow_sse:event/1 in cowlib guards the id and event fields against \n but not against bare \r, and the internal prefix_lines/2 function used for data and comment fields splits only on \n. Because the SSE specification requires decoders to treat \r\n, \r, and \n as equivalent line terminators, an attacker who controls any of these fields can inject additional SSE lines and forge a complete event with an arbitrary event type and data payload on the receiving end. In typical deployments where browser EventSource clients or other SSE consumers dispatch on event.type and render event.data, this enables event splitting, client-side logic manipulation, and stored-XSS-equivalent behaviour when event data is inserted into the DOM. This issue affects cowlib from 2.6.0.

CVE-2026-43968 Affected ninenines cowlib Versions

1 component(s)
Fixed Versions:
2.16.1
Product / Package Ecosystem Affected Versions Fixed Version
cowlib
 Hex
≥ 2.6.0
< 2.16.1
2.16.1

References

NVD — CVE-2026-43968 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-43968
Security Fix Commit FIX COMMIT
https://github.com/ninenines/cowlib/commit/6165fc40efa159ba1cceee7e7981e790acba5d9c
cna.erlef.org/cves/cve-2026-43968... WEB
https://cna.erlef.org/cves/CVE-2026-43968.html
ninenines cowlib Source Repository REPOSITORY
https://github.com/ninenines/cowlib
ninenines cowlib Release RELEASE
https://github.com/ninenines/cowlib/releases/tag/2.16.1
osv.dev/vulnerability/eef-c... WEB
https://osv.dev/vulnerability/EEF-CVE-2026-43968

Frequently Asked Questions

What is CVE-2026-43968?
CVE-2026-43968 is a security vulnerability in ninenines cowlib involving Improper Neutralization of CRLF Sequences ('CRLF Injection') vulnerability allows SSE event splitting and injection via unvalidated field values under CWE-93: Improper Neutralization of CRLF Sequences ('CRLF Injection').
Which ninenines cowlib versions are affected?
Affected versions include releases prior to 2.16.1 across affected packages: cowlib.
What version fixes CVE-2026-43968?
Upgrading to 2.16.1 (or the latest patched release for your respective branch) resolves the vulnerability.
Is cowlib affected?
Yes, cowlib is affected in releases prior to 2.16.1. Upgrade your dependency to 2.16.1 or later.
What is the CVSS score of CVE-2026-43968?
CVE-2026-43968 has a CVSS v3.1 base score of 4.0 (MODERATE) with vector string CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:L/A:N.
What CWE is associated with CVE-2026-43968?
CVE-2026-43968 is classified under CWE-93: Improper Neutralization of CRLF Sequences ('CRLF Injection') (The product uses CRLF (carriage return line feeds) as a special element, e.g. to separate lines or records, but it does not neutralize or incorrectly neutralizes CRLF sequences from inputs.).
How can I check Hex dependencies for CVE-2026-43968?
Run the dependency tree command: 'inspect dependencies for cowlib'. 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-hv23-4qp7-8c8r",
  "modified" : "2026-06-08T20:16:50Z",
  "published" : "2026-05-11T21:31:34Z",
  "aliases" : [ "CVE-2026-43968" ],
  "summary" : "ninenines cowlib: Improper Neutralization of CRLF Sequences ('CRLF Injection') vulnerability allows SSE event splitting and injection via unvalidated field values",
  "details" : "Improper Neutralization of CRLF Sequences ('CRLF Injection') vulnerability in ninenines cowlib allows SSE event splitting and injection via unvalidated field values.\n\ncow_sse:event/1 in cowlib guards the id and event fields against \\n but not against bare \\r, and the internal prefix_lines/2 function used for data and comment fields splits only on \\n. Because the SSE specification requires decoders to treat \\r\\n, \\r, and \\n as equivalent line terminators, an attacker who controls any of these fields can inject additional SSE lines and forge a complete event with an arbitrary event type and data payload on the receiving end. In typical deployments where browser EventSource clients or other SSE consumers dispatch on event.type and render event.data, this enables event splitting, client-side logic manipulation, and stored-XSS-equivalent behaviour when event data is inserted into the DOM.\n\nThis issue affects cowlib from 2.6.0.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:L/A:N"
  }, {
    "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"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Hex",
      "name" : "cowlib"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "2.6.0"
      }, {
        "fixed" : "2.16.1"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-43968"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/ninenines/cowlib/commit/6165fc40efa159ba1cceee7e7981e790acba5d9c"
  }, {
    "type" : "WEB",
    "url" : "https://cna.erlef.org/cves/CVE-2026-43968.html"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/ninenines/cowlib"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/ninenines/cowlib/releases/tag/2.16.1"
  }, {
    "type" : "WEB",
    "url" : "https://osv.dev/vulnerability/EEF-CVE-2026-43968"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-93" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-18T16:47:11Z",
    "nvd_published_at" : "2026-05-11T19:16:25Z"
  }
}