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:*:*:*:*:*:*:*:*","versionStartIncluding":"2.9.0","vulnerable":true}],"negate":false,"operator":"OR"}]}],"credits":[{"lang":"en","type":"finder","value":"Peter Ullrich"}],"descriptions":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","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.
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.
"}],"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."}],"impacts":[{"capecId":"CAPEC-105","descriptions":[{"lang":"en","value":"CAPEC-105 HTTP Request Splitting"}]}],"metrics":[{"cvssV4_0":{"attackComplexity":"LOW","attackRequirements":"PRESENT","attackVector":"LOCAL","baseScore":2.1,"baseSeverity":"LOW","privilegesRequired":"NONE","subAvailabilityImpact":"NONE","subConfidentialityImpact":"NONE","subIntegrityImpact":"LOW","userInteraction":"NONE","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"},"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":{"dateUpdated":"2026-05-11T18:24:59.802Z","orgId":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","shortName":"EEF"},"references":[{"tags":["related","third-party-advisory"],"url":"https://cna.erlef.org/cves/CVE-2026-43969.html"},{"tags":["related"],"url":"https://osv.dev/vulnerability/EEF-CVE-2026-43969"},{"tags":["patch"],"url":"https://github.com/erlef/cowlib/commit/177953dd51540da11090666c1f007214127a1144"}],"source":{"discovery":"EXTERNAL"},"title":"Cookie Request Header Injection via Unvalidated Encoder in cow_cookie:cookie/1","workarounds":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","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."}],"x_generator":{"engine":"cvelib 1.8.0"}}},"cveMetadata":{"assignerOrgId":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","assignerShortName":"EEF","cveId":"CVE-2026-43969","datePublished":"2026-05-11T18:06:40.667Z","dateReserved":"2026-05-04T18:23:25.573Z","dateUpdated":"2026-05-11T18:55:26.121Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"},"nvd":{"publishedDate":"2026-05-11 19:16:25","lastModifiedDate":"2026-05-11 19:16:25","problem_types":["CWE-93","CWE-93 CWE-93 Improper Neutralization of CRLF Sequences ('CRLF Injection')"],"metrics":{"cvssMetricV40":[{"source":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","type":"Secondary","cvssData":{"version":"4.0","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/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","baseScore":2.1,"baseSeverity":"LOW","attackVector":"LOCAL","attackComplexity":"LOW","attackRequirements":"PRESENT","privilegesRequired":"NONE","userInteraction":"NONE","vulnConfidentialityImpact":"NONE","vulnIntegrityImpact":"LOW","vulnAvailabilityImpact":"NONE","subConfidentialityImpact":"NONE","subIntegrityImpact":"LOW","subAvailabilityImpact":"NONE","exploitMaturity":"NOT_DEFINED","confidentialityRequirement":"NOT_DEFINED","integrityRequirement":"NOT_DEFINED","availabilityRequirement":"NOT_DEFINED","modifiedAttackVector":"NOT_DEFINED","modifiedAttackComplexity":"NOT_DEFINED","modifiedAttackRequirements":"NOT_DEFINED","modifiedPrivilegesRequired":"NOT_DEFINED","modifiedUserInteraction":"NOT_DEFINED","modifiedVulnConfidentialityImpact":"NOT_DEFINED","modifiedVulnIntegrityImpact":"NOT_DEFINED","modifiedVulnAvailabilityImpact":"NOT_DEFINED","modifiedSubConfidentialityImpact":"NOT_DEFINED","modifiedSubIntegrityImpact":"NOT_DEFINED","modifiedSubAvailabilityImpact":"NOT_DEFINED","Safety":"NOT_DEFINED","Automatable":"NOT_DEFINED","Recovery":"NOT_DEFINED","valueDensity":"NOT_DEFINED","vulnerabilityResponseEffort":"NOT_DEFINED","providerUrgency":"NOT_DEFINED"}}]},"configurations":[]},"legacy_mitre":{"record":{"CveYear":"2026","CveId":"43969","Ordinal":"1","Title":"Cookie Request Header Injection via Unvalidated Encoder in cow_c","CVE":"CVE-2026-43969","Year":"2026"},"notes":[{"CveYear":"2026","CveId":"43969","Ordinal":"1","NoteData":"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.","Type":"Description","Title":"Cookie Request Header Injection via Unvalidated Encoder in cow_c"}]}}}