WebSocket 1-byte continuation frames bypass `max_fragmented_message_size` in Bandit
- Published
- Last modified
- Where the record stands: published, rejected by its publisher, or superseded by another id.What do these mean? →
- published
- Whether CISA lists it in its Known Exploited Vulnerabilities catalog: proof that attackers are using it.What do these mean? →
- Not listed in CISA KEV
- Fix
- Fixed in 1.14.0
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
- Exploitation: none
- Automatable: yes
- Technical impact: partial
Summary
Bandit, an Elixir web server for handling HTTP and WebSocket connections, is affected. A remote, unauthenticated attacker can send a WebSocket message split into many tiny fragments, which can consume large amounts of server memory and potentially exhaust it, even though the configured fragment size limit is meant to prevent this.
Summarized by anthropic/claude-haiku-5.5. Verify details against the original sources.
Read the original description
Allocation of Resources Without Limits or Throttling vulnerability in the WebSocket fragment reassembly of mtrudel bandit allows an unauthenticated remote attacker to exhaust server memory via a fragmented message made of many 1-byte continuation frames. Bandit.WebSocket.Connection checks max_fragmented_message_size against the payload bytes received, but keeps every non-final continuation frame as a new list cell around its own binary, and nothing limits the number of fragments. A 1-byte fragment costs 7 bytes on the wire but about 150 to 170 bytes of server memory, so one connection can hold about 150 times the configured limit, roughly 1.2 to 1.4 GB at the default 8 MB. Ping frames between fragments keep the connection alive past the idle timeout. This issue affects bandit: from 1.11.0 before 1.14.0.
Timeline
- CVE published
- First seen by cve.now
- CISA SSVC assessment
Exploitation: none · Automatable: yes · Technical impact: partial
- Record last updated
Affected versions
- bandit
From 1.11.0 · fixed in 1.14.0
- mtrudel/bandit
From 21612c7c7b1ce43eccd36d3af3a2299d23513667 · fixed in 220b9dfd27f9a21305be2afc75cbe585ddc24e7a