CVE-2026-39804

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.

CVSS

No CVSS.

References

Link	Resource
https://cna.erlef.org/cves/CVE-2026-39804.html
https://github.com/mtrudel/bandit/commit/8156921a51e684a951221da7bc30a70a022f722e
https://github.com/mtrudel/bandit/security/advisories/GHSA-frh3-6pv6-rc8j
https://osv.dev/vulnerability/EEF-CVE-2026-39804
https://github.com/mtrudel/bandit/security/advisories/GHSA-frh3-6pv6-rc8j

Configurations

No configuration.

History

02 May 2026, 02:16

Type	Values Removed	Values Added
References	~~() https://github.com/mtrudel/bandit/security/advisories/GHSA-frh3-6pv6-rc8j -~~	() https://github.com/mtrudel/bandit/security/advisories/GHSA-frh3-6pv6-rc8j -

01 May 2026, 21:16

Type	Values Removed	Values Added
New CVE

Information

Published : 2026-05-01 21:16

Updated : 2026-05-05 19:37

NVD link : CVE-2026-39804

Mitre link : CVE-2026-39804

CVE.ORG link : CVE-2026-39804

JSON object : View

Products Affected

No product.

CWE

CWE-770

Allocation of Resources Without Limits or Throttling

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