CVE-2026-39803

Description

Allocation of Resources Without Limits or Throttling vulnerability in mtrudel bandit allows unauthenticated remote denial of service via memory exhaustion. The chunked clause of 'Elixir.Bandit.HTTP1.Socket':read_data/2 in lib/bandit/http1/socket.ex ignores the caller-supplied :length option when reading HTTP/1 chunked request bodies. Instead of capping the accumulated body at the configured limit (e.g. Plug.Parsers' default 8 MB), do_read_chunked_data!/5 buffers every received chunk into an iolist unconditionally and materializes the entire body as a single binary. The function always returns {:ok, body, ...}, so callers cannot interpose a 413 response. Because Plug.Parsers runs before routing and authentication in the standard Phoenix endpoint, an unauthenticated attacker needs no valid route or credentials. Sending a single Transfer-Encoding: chunked POST request with an arbitrarily large body to any path causes the BEAM process to exhaust available memory and be terminated by the OS OOM killer. The content-length path in the same function correctly enforces the limit and is not affected. This issue affects bandit: from 1.4.0 before 1.11.1.

CVSS 3.1 breakdown

Affected products

Remediation

References

• https://cna.erlef.org/cves/CVE-2026-39803.htmlThird Party Advisory
• https://github.com/mtrudel/bandit/commit/ae3520dfdbfab115c638f8c7f6f6b805db34e1abPatch
• https://github.com/mtrudel/bandit/security/advisories/GHSA-9q9q-324x-93r2ExploitVendor Advisory
• https://osv.dev/vulnerability/EEF-CVE-2026-39803Third Party Advisory

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