{"id":"CVE-2026-43969","state":"PUBLISHED","title":"Cookie Request Header Injection via Unvalidated Encoder in cow_cookie:cookie/1","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.\n\ncow_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.\n\nThis issue affects cowlib: from 2.9.0 before 2.21.0.","publishedAt":"2026-05-11T18:06:40.667Z","updatedAt":"2026-10-09T06:57:15.234Z","severity":{"score":2.1,"label":"Low","version":"4.0","vector":"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","source":"EEF"},"assigner":"EEF","products":["ninenines cowlib"],"affected":[{"vendor":"ninenines","product":"cowlib","packageName":"cowlib","packageURL":"pkg:hex/cowlib","defaultStatus":"unaffected","versions":[{"version":"2.9.0","status":"affected","lessThan":"2.21.0","versionType":"semver"}],"collectionURL":"https://repo.hex.pm","cpes":["cpe:2.3:a:ninenines:cowlib:*:*:*:*:*:*:*:*"],"modules":["cow_cookie"],"programFiles":["src/cow_cookie.erl"],"programRoutines":[{"name":"cow_cookie:cookie/1"}],"repo":"https://github.com/ninenines/cowlib"},{"vendor":"ninenines","product":"cowlib","packageName":"ninenines/cowlib","packageURL":"pkg:github/ninenines/cowlib","defaultStatus":"unaffected","versions":[{"version":"f017f8a0ecbffd5033d9ab49bf180186f7a523a7","status":"affected","lessThan":"c17fd73945ef536cccecc492d286fb6b6d1c3307","versionType":"git"}],"collectionURL":"https://github.com","cpes":["cpe:2.3:a:ninenines:cowlib:*:*:*:*:*:*:*:*"],"modules":["cow_cookie"],"programFiles":["src/cow_cookie.erl"],"programRoutines":[{"name":"cow_cookie:cookie/1"}],"repo":"https://github.com/ninenines/cowlib"}],"references":["https://github.com/erlef/cowlib/commit/177953dd51540da11090666c1f007214127a1144","https://cna.erlef.org/cves/CVE-2026-43969.html","https://osv.dev/vulnerability/EEF-CVE-2026-43969","https://github.com/ninenines/cowlib/commit/f017f8a0ecbffd5033d9ab49bf180186f7a523a7","https://github.com/ninenines/cowlib/commit/c17fd73945ef536cccecc492d286fb6b6d1c3307"],"weaknesses":["CWE-93"],"ingestedAt":"2026-10-29T20:11:57.932Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/43xxx/CVE-2026-43969.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-43969","state":"PUBLISHED","datePublished":"2026-05-11T18:06:40.667Z","dateUpdated":"2026-10-09T06:57:15.234Z","assignerShortName":"EEF","assignerOrgId":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","dateReserved":"2026-05-04T18:23:25.573Z"},"containers":{"cna":{"title":"Cookie Request Header Injection via Unvalidated Encoder in cow_cookie:cookie/1","descriptions":[{"lang":"en","value":"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.\n\ncow_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.\n\nThis issue affects cowlib: from 2.9.0 before 2.21.0."}],"affected":[{"vendor":"ninenines","product":"cowlib","packageName":"cowlib","packageURL":"pkg:hex/cowlib","defaultStatus":"unaffected","versions":[{"version":"2.9.0","status":"affected","lessThan":"2.21.0","versionType":"semver"}],"collectionURL":"https://repo.hex.pm","cpes":["cpe:2.3:a:ninenines:cowlib:*:*:*:*:*:*:*:*"],"modules":["cow_cookie"],"programFiles":["src/cow_cookie.erl"],"programRoutines":[{"name":"cow_cookie:cookie/1"}],"repo":"https://github.com/ninenines/cowlib"},{"vendor":"ninenines","product":"cowlib","packageName":"ninenines/cowlib","packageURL":"pkg:github/ninenines/cowlib","defaultStatus":"unaffected","versions":[{"version":"f017f8a0ecbffd5033d9ab49bf180186f7a523a7","status":"affected","lessThan":"c17fd73945ef536cccecc492d286fb6b6d1c3307","versionType":"git"}],"collectionURL":"https://github.com","cpes":["cpe:2.3:a:ninenines:cowlib:*:*:*:*:*:*:*:*"],"modules":["cow_cookie"],"programFiles":["src/cow_cookie.erl"],"programRoutines":[{"name":"cow_cookie:cookie/1"}],"repo":"https://github.com/ninenines/cowlib"}],"references":[{"url":"https://github.com/erlef/cowlib/commit/177953dd51540da11090666c1f007214127a1144","name":"GitHub Advisory","tags":["patch"]},{"url":"https://cna.erlef.org/cves/CVE-2026-43969.html","name":"EEF CNA record for CVE-2026-43969","tags":["related","third-party-advisory"]},{"url":"https://osv.dev/vulnerability/EEF-CVE-2026-43969","name":"OSV record EEF-CVE-2026-43969","tags":["related"]},{"url":"https://github.com/ninenines/cowlib/commit/f017f8a0ecbffd5033d9ab49bf180186f7a523a7","name":"Introducing commit f017f8a in ninenines/cowlib","tags":["related"]},{"url":"https://github.com/ninenines/cowlib/commit/c17fd73945ef536cccecc492d286fb6b6d1c3307","name":"Fix commit c17fd73 in ninenines/cowlib","tags":["patch"]}],"metrics":[{"cvssV4_0":{"Automatable":"NOT_DEFINED","Recovery":"NOT_DEFINED","Safety":"NOT_DEFINED","attackComplexity":"LOW","attackRequirements":"PRESENT","attackVector":"LOCAL","baseScore":2.1,"baseSeverity":"LOW","privilegesRequired":"NONE","providerUrgency":"NOT_DEFINED","subAvailabilityImpact":"NONE","subConfidentialityImpact":"NONE","subIntegrityImpact":"LOW","userInteraction":"NONE","valueDensity":"NOT_DEFINED","vectorString":"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","version":"4.0","vulnAvailabilityImpact":"NONE","vulnConfidentialityImpact":"NONE","vulnIntegrityImpact":"LOW","vulnerabilityResponseEffort":"NOT_DEFINED"},"format":"CVSS","scenarios":[{"lang":"en","value":"GENERAL"}]}],"problemTypes":[{"descriptions":[{"cweId":"CWE-93","description":"CWE-93 Improper Neutralization of CRLF Sequences ('CRLF Injection')","lang":"en","type":"CWE"}]}],"providerMetadata":{"shortName":"EEF","orgId":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","dateUpdated":"2026-10-09T06:57:15.234Z"},"configurations":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","value":"<p>The application must pass attacker-controlled bytes as cookie names or values to <code>cow_cookie:cookie/1</code>. Applications that construct cookie lists exclusively from trusted, application-controlled values are not affected.</p>"},{"base64":false,"type":"text/markdown","value":"The application must pass attacker-controlled bytes as cookie names or values to `cow_cookie:cookie/1`. Applications that construct cookie lists exclusively from trusted, application-controlled values are not affected."}],"value":"The application must pass attacker-controlled bytes as cookie names or values to cow_cookie:cookie/1. Applications that construct cookie lists exclusively from trusted, application-controlled values are not affected."}],"cpeApplicability":[{"nodes":[{"cpeMatch":[{"criteria":"cpe:2.3:a:ninenines:cowlib:*:*:*:*:*:*:*:*","versionEndExcluding":"2.21.0","versionStartIncluding":"2.9.0","vulnerable":true}],"negate":false,"operator":"OR"}],"operator":"AND"}],"credits":[{"lang":"en","type":"finder","value":"Peter Ullrich"},{"lang":"en","type":"remediation developer","value":"Loïc Hoguin"},{"lang":"en","type":"coordinator","value":"Jonatan Männchen / EEF"}],"impacts":[{"capecId":"CAPEC-105","descriptions":[{"lang":"en","value":"CAPEC-105 HTTP Request Splitting"}]}],"source":{"discovery":"EXTERNAL"},"workarounds":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","value":"<p>Validate inputs into <code>cow_cookie:cookie/1</code> to only include valid cookie name and value characters as defined in RFC 6265 Section 4.1.1 before passing them to the function.</p>"},{"base64":false,"type":"text/markdown","value":"Validate inputs into `cow_cookie:cookie/1` to only include valid cookie name and value characters as defined in RFC 6265 Section 4.1.1 before passing them to the function."}],"value":"Validate inputs into cow_cookie:cookie/1 to only include valid cookie name and value characters as defined in RFC 6265 Section 4.1.1 before passing them to the function."}]},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-05-11T18:55:16.028478Z","id":"CVE-2026-43969","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-05-11T18:55:26.121Z"}}]}}}