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VulnerabilityPublished Updated

CVE-2026-43969: ninenines cowlib · CRLF Injection

Affects ninenines cowlibSource CVE Database V5

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Not known to be exploited · CVSS 2.1 Low : upgrade to 2.21.0 when convenient.

Data as of 30 Oct 2026, 11:52 UTC

CVSS 4.0 base score
2.1Low
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.1% chance of exploitation in 30 days – higher than 3% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 2.21.0, c17fd73945ef536cccecc492d286fb6b6d1c3307
CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:L/SA:N

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 11 May 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 30 Oct 2026.

What to do

Upgrade cowlib to 2.21.0; cowlib to c17fd73945ef536cccecc492d286fb6b6d1c3307.

Affected software

ProductAffectedFixed in
nineninescowlibAffected
  • >=2.9.0 <2.21.0
Fixed in
  • 2.21.0
nineninescowlibAffected
  • ≥ f017f8a0ecbffd5033d9ab49bf180186f7a523a7, < c17fd73945ef536cccecc492d286fb6b6d1c3307
Fixed in
  • c17fd73945ef536cccecc492d286fb6b6d1c3307
Hexcowlibpkg:hex/cowlibOther threatsAffected
  • =2.9.0
Fixed in–
Hexcowlibpkg:hex/cowlibOther threatsAffected
  • >=2.9.0 <2.21.0
Fixed in
  • 2.21.0

CPE configurations (1)

  • cpe:2.3:a:ninenines:cowlib:*:*:*:*:*:*:*:*

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Since the decoder and setcookie functions already validate these characters, avoiding use of the vulnerable encoder or implementing additional input validation on cookie names and values may reduce risk until an official fix is released.

Description

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.

References

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