CVE-2026-43968 CR Injection in SSE Encoder Enables Event Splitting via cow_sse:event/1
Attackers can inject CRLF sequences in SSE events to forge arbitrary event types and data, potentially leading to client-side code execution or XSS.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-43968?
CVE-2026-43968 is a medium-severity vulnerability in ninenines cowlib, published on 11 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-93
Which versions are affected by CVE-2026-43968?
3 open source packages ship an affected version, including cowlib. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
cowlib Hex | From 2.6.0 | 2.16.1 |
cowlib Hex | From 2.6.0 | 2.16.1 |
cowlib Hex | From 2.6.0 | 2.16.1 |
Products include Ninenines Cowlib.
How do I fix CVE-2026-43968?
Upgrade cowlib to 2.16.1 or later.
Is CVE-2026-43968 being exploited?
There is no known exploitation of CVE-2026-43968 in the wild and no public exploit code.
Other vulnerabilities in ninenines cowlib
Sources
Also known as AZL-86793, EEF-CVE-2026-43968, GHSA-hv23-4qp7-8c8r.