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.
References
| Link | Resource |
|---|---|
| https://cna.erlef.org/cves/CVE-2026-39803.html | Third Party Advisory |
| https://github.com/mtrudel/bandit/commit/ae3520dfdbfab115c638f8c7f6f6b805db34e1ab | Patch |
| https://github.com/mtrudel/bandit/security/advisories/GHSA-9q9q-324x-93r2 | Exploit Vendor Advisory |
| https://osv.dev/vulnerability/EEF-CVE-2026-39803 | Third Party Advisory |
| https://github.com/mtrudel/bandit/security/advisories/GHSA-9q9q-324x-93r2 | Exploit Vendor Advisory |
Configurations
History
21 May 2026, 15:23
| Type | Values Removed | Values Added |
|---|---|---|
| CPE | cpe:2.3:a:mtrudel:bandit:*:*:*:*:*:*:*:* | |
| First Time |
Mtrudel bandit
Mtrudel |
|
| References | () https://cna.erlef.org/cves/CVE-2026-39803.html - Third Party Advisory | |
| References | () https://github.com/mtrudel/bandit/commit/ae3520dfdbfab115c638f8c7f6f6b805db34e1ab - Patch | |
| References | () https://github.com/mtrudel/bandit/security/advisories/GHSA-9q9q-324x-93r2 - Exploit, Vendor Advisory | |
| References | () https://osv.dev/vulnerability/EEF-CVE-2026-39803 - Third Party Advisory | |
| CVSS |
v2 : v3 : |
v2 : unknown
v3 : 7.5 |
13 May 2026, 16:16
| Type | Values Removed | Values Added |
|---|---|---|
| New CVE |
Information
Published : 2026-05-13 14:17
Updated : 2026-05-21 15:23
NVD link : CVE-2026-39803
Mitre link : CVE-2026-39803
CVE.ORG link : CVE-2026-39803
JSON object : View
Products Affected
mtrudel
- bandit
CWE
CWE-770
Allocation of Resources Without Limits or Throttling