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Resource Allocation Without LimitsWeakness · CWE-770

CVE-2026-39804

HIGH · 8.2 CVSS v4.0 Published 2026-05-01
Patch available
A vendor patch is available. No clean upgrade release — apply the published patch.
See remediation →
91/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click Patch available

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis
How this class of weakness works · CWE-770

The application allocates memory, connections, or handles in response to a request without enforcing any cap, so a modest amount of malicious traffic exhausts the resource and denies service to everyone else. The fix is enforcing quotas, limits, and timeouts on what any single request or client can consume.

General guidance for the resource allocation without limits class — the official description and references above are authoritative for this specific CVE. Want a bespoke review and a reviewed fix? Ask our team →

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
Authentication
X
User interaction
None
Scope
X

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Patch available Apply the vendor patch
Vendor patch github.com →
Recommended fix High confidence

bandit 1.11.0

  1. Update the bandit dependency in mix.exs to require version 1.11.0 or later (e.g., {:bandit, "~> 1.11.0"})
  2. Run `mix deps.get` to fetch the updated Bandit version
  3. Run `mix deps.compile` to recompile the dependency
  4. Verify the application starts successfully and WebSocket functionality works as expected
  5. If running in production, monitor memory usage during WebSocket connections to confirm the fix is effective

Generated from the published advisory — verify against the referenced sources before acting.

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-39804 in production — separate from our analysis above.

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