CVE-2026-42788 HTTP/2 frame size limit checked after body is buffered in bandit
Unauthenticated attackers can cause memory exhaustion and denial of service by sending oversized HTTP/2 frames that bypass size limits.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-42788?
CVE-2026-42788 is a medium-severity denial of service 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
Allocation of Resources Without Limits or Throttling vulnerability in mtrudel bandit allows unauthenticated memory exhaustion via oversized HTTP/2 frames.
'Elixir.Bandit.HTTP2.Frame':deserialize/2 in lib/bandit/http2/frame.ex checks the SETTINGS_MAX_FRAME_SIZE limit only after pattern-matching payload::binary-size(length), which requires the entire frame body to be present in memory before either the accept or reject clause can fire. A peer that announces a frame length up to the 24-bit maximum (~16 MiB) causes the server to buffer that entire body before the size guard is evaluated, regardless of the max_frame_size negotiated during the HTTP/2 handshake (default 16 KiB per RFC 9113).
An unauthenticated attacker holding many concurrent connections can force the server to buffer far more memory than the negotiated frame size limit should permit, leading to memory pressure and potential denial of service.
This issue affects bandit: from 0.3.6 before 1.11.0.
Weakness: CWE-770
Which versions are affected by CVE-2026-42788?
3 open source packages ship an affected version, including bandit.
| Package | Affected | Fixed in |
|---|---|---|
bandit Hex | From 0.3.5 | 1.11.0 |
bandit Hex | From 0.3.5 | 1.11.0 |
bandit Hex | From 0.3.6 | 1.11.0 |
How do I fix CVE-2026-42788?
Upgrade bandit to 1.11.0 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-42788 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-42788 exists.
Sources
Also known as EEF-CVE-2026-42788, GHSA-q6v9-r226-v65f.