8.7
HIGH CVSS 4.0
CVE-2026-39803
HTTP/1 chunked body reader ignores length cap in bandit
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.

INFO

Published Date :

May 13, 2026, 1:36 p.m.

Last Modified :

May 13, 2026, 1:48 p.m.

Remotely Exploit :

Yes !

Source :

EEF
Affected Products

The following products are affected by CVE-2026-39803 vulnerability. Even if cvefeed.io is aware of the exact versions of the products that are affected, the information is not represented in the table below.

No affected product recoded yet

CVSS Scores
The Common Vulnerability Scoring System is a standardized framework for assessing the severity of vulnerabilities in software and systems. We collect and displays CVSS scores from various sources for each CVE.
Score Version Severity Vector Exploitability Score Impact Score Source
CVSS 4.0 HIGH 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
Solution
Update the Elixir Bandit library to a version that properly limits chunked request body sizes.
  • Update Elixir Bandit to version 1.11.1 or later.
  • Configure appropriate request body size limits.
  • Ensure all components handle resource limits correctly.

We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).

Results are limited to the first 15 repositories due to potential performance issues.

The following list is the news that have been mention CVE-2026-39803 vulnerability anywhere in the article.

EPSS is a daily estimate of the probability of exploitation activity being observed over the next 30 days. Following chart shows the EPSS score history of the vulnerability.