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VulnerabilityPublished Updated

CVE-2026-39804: mtrudel bandit · Unthrottled Resource Allocation

Affects mtrudel banditSource CVE Database V5

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Not known to be exploited · CVSS 8.2 High : upgrade to 1.11.0 soon.

Data as of 30 Oct 2026, 11:52 UTC

CVSS 4.0 base score
8.2High
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.7% chance of exploitation in 30 days – higher than 55% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 1.11.0, 8156921a51e684a951221da7bc30a70a022f722e
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 1 May 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 30 Oct 2026.

What to do

Upgrade bandit to 1.11.0; bandit to 8156921a51e684a951221da7bc30a70a022f722e.

Affected software

ProductAffectedFixed in
mtrudelbanditAffected
  • >=0.5.9 <1.11.0
Fixed in
  • 1.11.0
mtrudelbanditAffected
  • ≥ da4027cff7d2b80319e76fe7a32f84beceec490a, < 8156921a51e684a951221da7bc30a70a022f722e
Fixed in
  • 8156921a51e684a951221da7bc30a70a022f722e
Hexmtrudel/banditpkg:hex/mtrudel/banditOther threatsAffected
  • =0.5.9
Fixed in–
Hexbanditpkg:hex/banditOther threatsAffected
  • >=0.5.9 <1.11.0
Fixed in
  • 1.11.0

CPE configurations (1)

  • cpe:2.3:a:mtrudel:bandit:*:*:*:*:*:*:*:*

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Until a patch or official fix is available, mitigate by disabling WebSocket permessage-deflate compression in bandit (i.e., ensure websocket_options.compress and compress: true are not both enabled). Since stock Phoenix and LiveView applications default to compress: false, they are not affected unless explicitly configured otherwise.

Description

Allocation of Resources Without Limits or Throttling vulnerability in mtrudel bandit allows unauthenticated remote denial of service via memory exhaustion when WebSocket permessage-deflate compression is enabled. 'Elixir.Bandit.WebSocket.PerMessageDeflate':inflate/2 in lib/bandit/websocket/permessage_deflate.ex calls :zlib.inflate/2 with no output-size cap, then materializes the entire decompressed payload as a single binary via IO.iodata_to_binary/1. The websocket_options.max_frame_size option only bounds the on-the-wire (compressed) frame size, not the decompressed output. A high-ratio compressed frame (e.g.uniform data at ~1024:1 ratio) can stay well under any wire-size limit while forcing GiB-scale heap allocations in the connection process before any application code runs. An unauthenticated attacker who can open a WebSocket connection can send a single such frame to exhaust the BEAM node's memory and trigger an OOM kill. This vulnerability requires both Bandit's server-level websocket_options.compress and the per-upgrade compress: true option passed to WebSockAdapter.upgrade/4 to be enabled. Stock Phoenix and LiveView applications are not affected as they default to compress: false. This issue affects bandit: from 0.5.9 before 1.11.0.

References

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