High severity · published May 13, 2026
CVE-2026-39803
HTTP/1 chunked body reader ignores length cap in bandit
7.5
CVSS
0.6%
EPSS
No
On KEV
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 vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
None
Integrity
None
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.6% · higher than 51% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
BA
bandit · mtrudel
1.4.0 before 1.11.1; 903e209a521bc216b9f9065c01ae9a0cac2d5a10 before ae3520dfdbfab115c638f8c7f6f6b805db34e1ab · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-39803
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-39803
Third Party Advisory
https://cna.erlef.org/cves/CVE-2026-39803.html
Patch
https://github.com/mtrudel/bandit/commit/ae3520dfdbfab115c638f8c7f6f6b805db34e1ab
Exploit
https://github.com/mtrudel/bandit/security/advisories/GHSA-9q9q-324x-93r2
Third Party Advisory
https://osv.dev/vulnerability/EEF-CVE-2026-39803
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