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CVE-2026-43966VulnerabilityPublished Updated

cow_http_struct_hd:escape_string/2 · HTTP Response Splitting via Non-VCHAR Bytes

Affects MicrosoftSource GCVE Database

0
Authoritative record:CVE-2026-43966· Medium 6.3

Not known to be exploited · CVSS 6.3 Medium : upgrade to 4401b858f2229abb3ea115c60924f6c77e5f8aa3 when convenient.

Data as of 26 Oct 2026, 13:47 UTC

CVSS 4.0 base score
6.3Medium
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.2% chance of exploitation in 30 days – higher than 17% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 4401b858f2229abb3ea115c60924f6c77e5f8aa3
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 8 Jun 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponised: 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 26 Oct 2026.

What to do

Upgrade cowlib to 4401b858f2229abb3ea115c60924f6c77e5f8aa3.

Affected software

ProductAffectedFixed in
nineninescowlibAffected
  • >=2.9.0
Fixed in–
nineninescowlibAffected
  • ≥ a8b793db3d6ffe91d62f81baf41b1dab4cd78fb6, < 4401b858f2229abb3ea115c60924f6c77e5f8aa3
Fixed in
  • 4401b858f2229abb3ea115c60924f6c77e5f8aa3
Hexcowlibpkg:hex/cowlibOther threatsAffected
  • =2.9.0
Fixed in–
Hexcowlibpkg:hex/cowlibOther threatsAffected
  • >=2.9.0
Fixed in–

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

Description

To determine the support lifecycle for your software, see the Microsoft Support Lifecycle: https://support.microsoft.com/lifecycle

References

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