CVE-2026-43969

What it is

Improper Neutralization of CRLF Sequences ('CRLF Injection') vulnerability in ninenines cowlib allows HTTP request splitting and cookie smuggling via unvalidated cookie name and value fields. cow_cookie:cookie/1 in cowlib builds a client-side Cookie: request header from a list of name-value pairs without validating either field. An attacker who controls the cookie names or values passed to this function can inject ;, ,, CR, LF, or TAB characters into the serialized header. This enables two classes of attack: cookie smuggling within a single header (e.g. injecting ; admin=1 to introduce a phantom cookie that the receiving server treats as authentic) and HTTP request header splitting (injecting CRLF to append arbitrary headers or smuggle a complete second request against a shared upstream proxy). The decoder side (parse_cookie_name/1, parse_cookie_value/1) and setcookie/3 already validate and reject these characters; the encoder alone is missing the check. This issue affects cowlib: from 2.9.0 before 2.21.0.

At a glance

Exploitability

Can be exploited locally on the machine without logging in. Limited direct impact.

Exploit odds

0.1% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2026-05-11 19:16 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-10-26 20:10 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 0.1% in the next 30 days (EPSS).
• Severity: 2.1 LOW (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2026-05-11 19:16 UTC

Last modified

2026-10-26 20:10 UTC

Exploit probability

0.1% · EPSS, next 30 days

Weakness

CWE-93

Record status

Modified

Affected

• Ninenines Cowlib ≤ 2.16.1

Attack profile CVSS 4.0 · 2.1

Attack vector

Local

Complexity

Low

Attack requirements

Present

Privileges needed

None

User interaction

None

Confidentiality

None

Integrity

Low

Availability

None

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2026-43969.md and follow it. Check whether this project is affected by CVE-2026-43969. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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