CVE-2026-42786

Description

Allocation of Resources Without Limits or Throttling vulnerability in mtrudel bandit allows unauthenticated remote denial of service via memory exhaustion. The fragment reassembly path in 'Elixir.Bandit.WebSocket.Connection':handle_frame/3 in lib/bandit/websocket/connection.ex appends every incoming Continuation{fin: false} frame's payload to a per-connection iolist with no cumulative size cap. The existing max_frame_size option only bounds individual frames; a peer that streams an unbounded number of continuation frames without ever setting fin=1 grows BEAM heap linearly until the OS or a supervisor kills the process. Because the accumulation happens before WebSock.handle_in/2 is called, the application has no opportunity to interpose a size check. Phoenix Channels and LiveView both run over WebSock on Bandit, so a stock Phoenix application exposes this surface as soon as it accepts socket connections. This issue affects bandit: from 0.5.0 before 1.11.0.

PUBLISHED Reserved 2026-04-29 | Published 2026-05-01 | Updated 2026-05-04 | Assigner EEF

Problem types

CWE-770 Allocation of Resources Without Limits or Throttling

Product status

Credits

Peter Ullrich finder

Mat Trudel remediation developer

Jonatan Männchen analyst

References

github.com/...bandit/security/advisories/GHSA-pf94-94m9-536p exploit

github.com/...bandit/security/advisories/GHSA-pf94-94m9-536p vendor-advisory related

cna.erlef.org/cves/CVE-2026-42786.html related

osv.dev/vulnerability/EEF-CVE-2026-42786 related

github.com/...ommit/21612c7c7b1ce43eccd36d3af3a2299d23513667 patch

cve.org (CVE-2026-42786)

nvd.nist.gov (CVE-2026-42786)

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