CVE-2026-43968 Details
Description
Improper Neutralization of CRLF Sequences ('CRLF Injection') vulnerability in ninenines cowlib allows SSE event splitting and injection via unvalidated field values. cow_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. This issue affects cowlib from 2.6.0 before 2.16.1.
A CRLF injection vulnerability has been identified in ninenines cowlib version 2.6.0 and later. This issue arises from improper validation of field values in the SSE event handling function cow_sse:event/1. While the function correctly guards against newline characters in the id and event fields, it fails to validate carriage return characters. Additionally, the internal prefix_lines/2 function, which processes data and comment fields, only splits on newlines. As a result, an attacker can exploit this oversight by injecting additional SSE lines, effectively splitting events and manipulating client-side logic. This behavior is akin to stored cross-site scripting when the injected event data is rendered in the DOM.
Sanitize user-controlled values before sending them to cow_sse:event/1. Remove or reject any values that include carriage return or newline characters in the id, event, data, and comment fields. Ensure that all SSE field values come from trusted, application-controlled sources rather than user input.
Metrics
CVSS 4.0 Severity and Vector Strings:
CVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
CISA-ADP
Assessed May 11, 2026References to Advisories, Solutions, and Tools
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| URL | Source(s) | Tag(s) |
|---|---|---|
| https://cna.erlef.org/cves/CVE-2026-43968.html | EEF | Vendor Advisory |
| https://github.com/ninenines/cowlib/commit/6165fc40efa159ba1cceee7e7981e790acba5d9c | EEF | Patch |
| https://osv.dev/vulnerability/EEF-CVE-2026-43968 | EEF | Third Party Advisory |
Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-93 | Improper Neutralization of CRLF Sequences ('CRLF Injection') | EEF |
Affected Products
| Product | Versions |
|---|---|
| ninenines cowlib | >= 2.6.0, < 2.16.1 |
CPE
Remediation
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Change History
5 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Jun 17, 2026 | CVE Modified | EEF |
| Jun 17, 2026 | CVE Modified | CISA-ADP |
| May 21, 2026 | Initial Analysis | [email protected] |
| May 12, 2026 | CVE Modified | EEF |
| May 11, 2026 | New CVE Received | EEF |