CVE-2026-43968: CR Injection in SSE Encoder Enables Event Splitting via cow_sse:event/1
CR Injection in SSE Encoder Enables Event Splitting via cowsse:event/1
Other sources
Improper Neutralization of CRLF Sequences ('CRLF Injection') vulnerability in ninenines cowlib allows SSE event splitting and injection via unvalidated field values.
cowsse:event/1 in cowlib guards the id and event fields against \n but not against bare \r, and the internal prefixlines/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.
— MITRE
Affected Software
Remediation
Event History
Frequently Asked Questions
What is the severity of CVE-2026-43968?
CVE-2026-43968 is classified with a high severity due to its ability to enable event splitting and injection.
How do I fix CVE-2026-43968?
To fix CVE-2026-43968, ensure you are using cowlib versions outside of the affected range, specifically above version 2.16.1 or below 2.6.0.
What kind of attacks can be executed using CVE-2026-43968?
CVE-2026-43968 can be exploited to perform CRLF injection attacks, which may result in event splitting.
Which versions of cowlib are affected by CVE-2026-43968?
CVE-2026-43968 affects cowlib versions between 2.6.0 and 2.16.1 inclusive.
What does CVE-2026-43968 relate to in terms of functionality?
CVE-2026-43968 relates to the cow_sse:event/1 functionality where improper neutralization of input allows for injection vulnerabilities.