CVE-2026-39805 CL.CL HTTP request smuggling via duplicate Content-Length in bandit
An attacker can smuggle HTTP requests past security controls by exploiting inconsistent Content-Length header handling in the Bandit server.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-39805?
CVE-2026-39805 is a medium-severity vulnerability in mtrudel bandit, published on 1 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Inconsistent Interpretation of HTTP Requests vulnerability in mtrudel bandit allows HTTP request smuggling via duplicate Content-Length headers.
'Elixir.Bandit.Headers':get_content_length/1 in lib/bandit/headers.ex uses List.keyfind/3, which returns only the first matching header. When a request contains two Content-Length headers with different values, Bandit silently accepts it, uses the first value to read the body, and dispatches the remaining bytes as a second pipelined request on the same keep-alive connection. RFC 9112 §6.3 requires recipients to treat this as an unrecoverable framing error.
When Bandit sits behind a proxy that picks the last Content-Length value and forwards the request rather than rejecting it, an unauthenticated attacker can smuggle requests past edge WAF rules, path-based ACLs, rate limiting, and audit logging.
This issue affects bandit: before 1.11.0.
Weakness: CWE-444
Which versions are affected by CVE-2026-39805?
3 open source packages ship an affected version, including bandit.
| Package | Affected | Fixed in |
|---|---|---|
bandit Hex | All versions | 1.11.0 |
bandit Hex | All versions | 1.11.0 |
bandit Hex | From 0.1.0 | 1.11.0 |
How do I fix CVE-2026-39805?
Upgrade bandit to 1.11.0 or later.
Is CVE-2026-39805 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-39805 exists.
Sources
Also known as EEF-CVE-2026-39805, GHSA-c67r-gc9j-2qf7.