Weakness Type (CWE)

CWE-770 — CWE-770 Allocation of Resources Without Limits or Throttling

CAPEC

CVSS 4.0 Score

8.7

HIGH

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Vulnerability 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.

Affected

pkg:hex/bandit

Module Source File Routine
Bandit.WebSocket.Connection lib/bandit/websocket/connection.ex Bandit.WebSocket.Connection.handle_frame/3
Status Type Version Changes / Fixed in
affected semver ⓘ 0.5.0 < 1.11.0

pkg:github/mtrudel/bandit

Module Source File Routine
Bandit.WebSocket.Connection lib/bandit/websocket/connection.ex Bandit.WebSocket.Connection.handle_frame/3
Status Type Version Changes / Fixed in
affected git ⓘ 8909391f48 < 1.11.0

Configurations

The application must accept WebSocket connections. Applications that expose no WebSocket endpoints are not affected.

References

Credits

  • Finder: Peter Ullrich
  • Remediation developer: Mat Trudel
  • Analyst: Jonatan Männchen

CVE record as JSON:  GET /cves/CVE-2026-42786.json
OSV record as JSON:  GET /osv/EEF-CVE-2026-42786.json