CVE-2026-43966

Exploitation

Assessed, none found. CISA's assessment recorded neither public exploit code nor evidence of exploitation when it was made.

SSVC decision

• ExploitationnoneCISA recorded no public exploit code and no evidence of exploitation.
• AutomatablenoAt least one step from reconnaissance to exploitation cannot be reliably automated.
• Technical ImpactpartialSuccessful exploitation gives limited control of the vulnerable component.

CISA publishes the decision points, not a final SSVC decision. The decision also depends on mission and well-being impact, which is a property of your deployment rather than of the vulnerability.

EPSS probability

0.25% probability of exploitation activity in the next 30 days.

EPSS percentile

Equal to or higher than the score of 17.3% of scored records. A rank, not a probability.

NVD base score

6.3 (CVSS v4.0), scored by the NVD independently of the CNA.

NVD CVSS vector

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/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

NVD analysis status

Modified. NVD last modified this record on 2026-10-14.

Red Hat severity

No Red Hat rating. Red Hat rates the CVEs that affect its products.

Exploit-prediction scores from FIRST. Independent scoring and analysis status from the NVD. Vendor severity from Red Hat. Exploitation assessment and catalog membership from CISA.

Published

2026-06-08 16:34Z4 MO AGO

Last updated

2026-10-14 09:22Z15 DAYS AGO

Reserved

2026-05-04

Assigning CNA

EEF

Record state

PUBLISHED

Severity

Medium (CVSS 6.3)

CNA CVSS vector

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

Weaknesses

• CWE-113Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting')Variant

Data version

5.2

Document digest

2cea41eb75e80f9120550ead326d86a29683661f992db81840886fddaa62fdf6

• github.comcowboy: Add invalid_response_headers HTTP/1 optionhttps://github.com/ninenines/cowboy/commit/f77cb9b5e730e300fffb551db1ba5d1c4ed878efmitigation
• cna.erlef.orgEEF CNA record for CVE-2026-43966https://cna.erlef.org/cves/CVE-2026-43966.htmlrelatedthird-party-advisory
• osv.devOSV record EEF-CVE-2026-43966https://osv.dev/vulnerability/EEF-CVE-2026-43966related
• github.comgun: Add invalid_request_headers request optionhttps://github.com/ninenines/gun/commit/4f35609eb37109b106a863fc9ba83d7ee64e3e42mitigation
• github.comIntroducing commit a8b793d in ninenines/cowlibhttps://github.com/ninenines/cowlib/commit/a8b793db3d6ffe91d62f81baf41b1dab4cd78fb6related
• github.comFix commit 4401b85 in ninenines/cowlibhttps://github.com/ninenines/cowlib/commit/4401b858f2229abb3ea115c60924f6c77e5f8aa3patch