{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2026-43971", "assignerOrgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "state": "PUBLISHED", "assignerShortName": "EEF", "dateReserved": "2026-05-04T18:23:25.574Z", "datePublished": "2026-08-18T09:01:53.199Z", "dateUpdated": "2026-08-18T09:01:53.199Z"}, "containers": {"cna": {"affected": [{"collectionURL": "https://repo.hex.pm", "cpes": ["cpe:2.3:a:ninenines:cowlib:*:*:*:*:*:*:*:*"], "defaultStatus": "unaffected", "modules": ["cow_link"], "packageName": "cowlib", "packageURL": "pkg:hex/cowlib", "product": "cowlib", "programFiles": ["src/cow_link.erl"], "programRoutines": [{"name": "cow_link:link/1"}, {"name": "cow_link:do_link/1"}, {"name": "cow_link:escape/2"}], "repo": "https://github.com/ninenines/cowlib", "vendor": "ninenines", "versions": [{"lessThan": "*", "status": "affected", "version": "2.9.0", "versionType": "semver"}]}, {"collectionURL": "https://github.com", "cpes": ["cpe:2.3:a:ninenines:cowlib:*:*:*:*:*:*:*:*"], "defaultStatus": "unaffected", "modules": ["cow_link"], "packageName": "ninenines/cowlib", "packageURL": "pkg:github/ninenines/cowlib", "product": "cowlib", "programFiles": ["src/cow_link.erl"], "programRoutines": [{"name": "cow_link:link/1"}, {"name": "cow_link:do_link/1"}, {"name": "cow_link:escape/2"}], "repo": "https://github.com/ninenines/cowlib", "vendor": "ninenines", "versions": [{"lessThan": "*", "status": "affected", "version": "485d58dfa91b91d98135dc95e5615f421715dae5", "versionType": "git"}]}], "configurations": [{"lang": "en", "supportingMedia": [{"base64": false, "type": "text/html", "value": "<p>The application must pass values that originate from, or can be influenced by, untrusted input into <code>cow_link:link/1</code> \u2014 specifically the target URI, rel value, or attribute keys. Applications that construct Link entries exclusively from trusted, application-controlled values are not affected.</p>"}, {"base64": false, "type": "text/markdown", "value": "The application must pass values that originate from, or can be influenced by, untrusted input into `cow_link:link/1` \u2014 specifically the target URI, rel value, or attribute keys. Applications that construct Link entries exclusively from trusted, application-controlled values are not affected."}], "value": "The application must pass values that originate from, or can be influenced by, untrusted input into cow_link:link/1 \u2014 specifically the target URI, rel value, or attribute keys. Applications that construct Link entries 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"}], "operator": "AND"}], "credits": [{"lang": "en", "type": "finder", "value": "Peter Ullrich"}], "descriptions": [{"lang": "en", "supportingMedia": [{"base64": false, "type": "text/html", "value": "<p>Improper Encoding or Escaping of Output vulnerability in ninenines cowlib allows Link header directive smuggling via unescaped special characters in <code>cow_link:link/1</code>.</p>\n<p><code>cow_link:do_link/1</code> in cowlib interpolates the target URI, rel value, and attribute keys directly into the serialized <code>Link:</code> header value without escaping or token-grammar validation. A <code>&gt;</code> byte in target prematurely closes the URI slot, allowing an attacker to append additional link entries with attacker-chosen rel directives. A <code>\"</code> or <code>\\</code> in rel escapes the quoted string and opens new parameters. Any byte \u2014 including whitespace, <code>=</code>, and <code>\"</code> \u2014 in an attribute key is emitted verbatim. Because browsers act on <code>Link:</code> directives such as <code>rel=\"preconnect\"</code>, <code>rel=\"preload\"</code>, and <code>rel=\"prerender\"</code>, an attacker who can influence these fields in an application that round-trips parsed Link headers through <code>cow_link:link/1</code> can force victim browsers to make out-of-band connections to attacker-controlled origins.</p>\n<p>This issue affects cowlib: from 2.9.0 onward.</p>"}, {"base64": false, "type": "text/markdown", "value": "Improper Encoding or Escaping of Output vulnerability in ninenines cowlib allows Link header directive smuggling via unescaped special characters in `cow_link:link/1`.\n\n`cow_link:do_link/1` in cowlib interpolates the target URI, rel value, and attribute keys directly into the serialized `Link:` header value without escaping or token-grammar validation. A `>` byte in target prematurely closes the URI slot, allowing an attacker to append additional link entries with attacker-chosen rel directives. A `\"` or `\\` in rel escapes the quoted string and opens new parameters. Any byte \u2014 including whitespace, `=`, and `\"` \u2014 in an attribute key is emitted verbatim. Because browsers act on `Link:` directives such as `rel=\"preconnect\"`, `rel=\"preload\"`, and `rel=\"prerender\"`, an attacker who can influence these fields in an application that round-trips parsed Link headers through `cow_link:link/1` can force victim browsers to make out-of-band connections to attacker-controlled origins.\n\nThis issue affects cowlib: from 2.9.0 onward."}], "value": "Improper Encoding or Escaping of Output vulnerability in ninenines cowlib allows Link header directive smuggling via unescaped special characters in cow_link:link/1.\n\ncow_link:do_link/1 in cowlib interpolates the target URI, rel value, and attribute keys directly into the serialized Link: header value without escaping or token-grammar validation. A > byte in target prematurely closes the URI slot, allowing an attacker to append additional link entries with attacker-chosen rel directives. A \" or \\ in rel escapes the quoted string and opens new parameters. Any byte \u2014 including whitespace, =, and \" \u2014 in an attribute key is emitted verbatim. Because browsers act on Link: directives such as rel=\"preconnect\", rel=\"preload\", and rel=\"prerender\", an attacker who can influence these fields in an application that round-trips parsed Link headers through cow_link:link/1 can force victim browsers to make out-of-band connections to attacker-controlled origins.\n\nThis issue affects cowlib: from 2.9.0 onward."}], "impacts": [{"capecId": "CAPEC-137", "descriptions": [{"lang": "en", "value": "CAPEC-137 Parameter Injection"}]}], "metrics": [{"cvssV4_0": {"Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "Safety": "NOT_DEFINED", "attackComplexity": "LOW", "attackRequirements": "PRESENT", "attackVector": "NETWORK", "baseScore": 6.3, "baseSeverity": "MEDIUM", "privilegesRequired": "NONE", "providerUrgency": "NOT_DEFINED", "subAvailabilityImpact": "NONE", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "LOW", "userInteraction": "NONE", "valueDensity": "NOT_DEFINED", "vectorString": "CVSS:4.0/AV:N/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-116", "description": "CWE-116 Improper Encoding or Escaping of Output", "lang": "en", "type": "CWE"}]}], "providerMetadata": {"orgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "shortName": "EEF", "dateUpdated": "2026-08-18T09:01:53.199Z"}, "references": [{"tags": ["related", "third-party-advisory"], "url": "https://cna.erlef.org/cves/CVE-2026-43971.html"}, {"tags": ["related"], "url": "https://osv.dev/vulnerability/EEF-CVE-2026-43971"}], "source": {"discovery": "EXTERNAL"}, "title": "Link Header Directive Smuggling via Unescaped target/rel/Attribute Keys in cow_link:link/1", "workarounds": [{"lang": "en", "supportingMedia": [{"base64": false, "type": "text/html", "value": "<p>Sanitize values before passing them to <code>cow_link:link/1</code>: reject or strip any target value containing <code>&gt;</code>, any rel value containing <code>\"</code> or <code>\\</code>, and any attribute key containing characters outside the HTTP token grammar. Alternatively, ensure all Link entry fields are derived exclusively from trusted, application-controlled values rather than untrusted input.</p>"}, {"base64": false, "type": "text/markdown", "value": "Sanitize values before passing them to `cow_link:link/1`: reject or strip any target value containing `>`, any rel value containing `\"` or `\\`, and any attribute key containing characters outside the HTTP token grammar. Alternatively, ensure all Link entry fields are derived exclusively from trusted, application-controlled values rather than untrusted input."}], "value": "Sanitize values before passing them to cow_link:link/1: reject or strip any target value containing >, any rel value containing \" or \\, and any attribute key containing characters outside the HTTP token grammar. Alternatively, ensure all Link entry fields are derived exclusively from trusted, application-controlled values rather than untrusted input."}]}}}

{}

{"affected": [{"affectedData": [{"collectionURL": "https://repo.hex.pm", "cpes": ["cpe:2.3:a:ninenines:cowlib:*:*:*:*:*:*:*:*"], "defaultStatus": "unaffected", "modules": ["cow_link"], "packageName": "cowlib", "packageURL": "pkg:hex/cowlib", "product": "cowlib", "programFiles": ["src/cow_link.erl"], "programRoutines": [{"name": "cow_link:link/1"}, {"name": "cow_link:do_link/1"}, {"name": "cow_link:escape/2"}], "repo": "https://github.com/ninenines/cowlib", "vendor": "ninenines", "versions": [{"lessThan": "*", "status": "affected", "version": "2.9.0", "versionType": "semver"}]}, {"collectionURL": "https://github.com", "cpes": ["cpe:2.3:a:ninenines:cowlib:*:*:*:*:*:*:*:*"], "defaultStatus": "unaffected", "modules": ["cow_link"], "packageName": "ninenines/cowlib", "packageURL": "pkg:github/ninenines/cowlib", "product": "cowlib", "programFiles": ["src/cow_link.erl"], "programRoutines": [{"name": "cow_link:link/1"}, {"name": "cow_link:do_link/1"}, {"name": "cow_link:escape/2"}], "repo": "https://github.com/ninenines/cowlib", "vendor": "ninenines", "versions": [{"lessThan": "*", "status": "affected", "version": "485d58dfa91b91d98135dc95e5615f421715dae5", "versionType": "git"}]}], "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db"}], "cveTags": [], "descriptions": [{"lang": "en", "value": "Improper Encoding or Escaping of Output vulnerability in ninenines cowlib allows Link header directive smuggling via unescaped special characters in cow_link:link/1.\n\ncow_link:do_link/1 in cowlib interpolates the target URI, rel value, and attribute keys directly into the serialized Link: header value without escaping or token-grammar validation. A > byte in target prematurely closes the URI slot, allowing an attacker to append additional link entries with attacker-chosen rel directives. A \" or \\ in rel escapes the quoted string and opens new parameters. Any byte \u2014 including whitespace, =, and \" \u2014 in an attribute key is emitted verbatim. Because browsers act on Link: directives such as rel=\"preconnect\", rel=\"preload\", and rel=\"prerender\", an attacker who can influence these fields in an application that round-trips parsed Link headers through cow_link:link/1 can force victim browsers to make out-of-band connections to attacker-controlled origins.\n\nThis issue affects cowlib: from 2.9.0 onward."}], "id": "CVE-2026-43971", "lastModified": "2026-08-18T09:17:14.340", "metrics": {"cvssMetricV40": [{"cvssData": {"Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "Safety": "NOT_DEFINED", "attackComplexity": "LOW", "attackRequirements": "PRESENT", "attackVector": "NETWORK", "availabilityRequirement": "NOT_DEFINED", "baseScore": 6.3, "baseSeverity": "MEDIUM", "confidentialityRequirement": "NOT_DEFINED", "exploitMaturity": "NOT_DEFINED", "integrityRequirement": "NOT_DEFINED", "modifiedAttackComplexity": "NOT_DEFINED", "modifiedAttackRequirements": "NOT_DEFINED", "modifiedAttackVector": "NOT_DEFINED", "modifiedPrivilegesRequired": "NOT_DEFINED", "modifiedSubAvailabilityImpact": "NOT_DEFINED", "modifiedSubConfidentialityImpact": "NOT_DEFINED", "modifiedSubIntegrityImpact": "NOT_DEFINED", "modifiedUserInteraction": "NOT_DEFINED", "modifiedVulnAvailabilityImpact": "NOT_DEFINED", "modifiedVulnConfidentialityImpact": "NOT_DEFINED", "modifiedVulnIntegrityImpact": "NOT_DEFINED", "privilegesRequired": "NONE", "providerUrgency": "NOT_DEFINED", "subAvailabilityImpact": "NONE", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "LOW", "userInteraction": "NONE", "valueDensity": "NOT_DEFINED", "vectorString": "CVSS:4.0/AV:N/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", "version": "4.0", "vulnAvailabilityImpact": "NONE", "vulnConfidentialityImpact": "NONE", "vulnIntegrityImpact": "LOW", "vulnerabilityResponseEffort": "NOT_DEFINED"}, "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "type": "Secondary"}]}, "published": "2026-08-18T09:17:14.340", "references": [{"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "url": "https://cna.erlef.org/cves/CVE-2026-43971.html"}, {"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "url": "https://osv.dev/vulnerability/EEF-CVE-2026-43971"}], "sourceIdentifier": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "vulnStatus": "Received", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-116"}], "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "type": "Secondary"}]}

{}

{"affected": [{"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "[2.9.0,*]"}}, {"platform": null, "status": "affected", "versions": {"scheme": "code_commit", "value": "[485d58dfa91b91d98135dc95e5615f421715dae5,*]"}}], "enrichment": {"confidence": 95.0, "confidence_source": "inferred", "scores": [{"score": 95.0, "source": "inferred"}, {"score": 100.0, "source": "matching"}]}, "original": {"product": "cowlib", "source": "cna", "vendor": "ninenines"}, "product": "cowlib", "vendor": "ninenines"}, {"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "code_commit", "value": "[485d58dfa91b91d98135dc95e5615f421715dae5,*]"}}], "enrichment": {"confidence": 100.0, "confidence_source": "matching", "scores": [{"score": 100.0, "source": "matching"}]}, "original": {"product": "cowlib", "source": "cna", "vendor": "ninenines"}, "product": "cowlib", "vendor": "ninenines"}], "created": "2026-08-18T10:30:10.659599+00:00", "updated": "2026-08-18T10:30:10.756152+00:00", "vendors": ["ninenines", "ninenines$PRODUCT$cowlib"]}