CVE-2026-113436 PUBLISHED

Inefficient Algorithmic Complexity vulnerability in the header integer parser of mtrudel bandit allows an unauthenticated remote attacker to consume server CPU via a content-length value or a Host or :authority port made of thousands of digits.

Bandit.Headers.parse_integer/2 in lib/bandit/headers.ex builds the number one digit at a time with no limit on the digit count, allocating a new bignum at each step, so one value costs time quadratic in its length. It runs on raw request input over HTTP/1 and HTTP/2, before any range check. Over HTTP/2, a 4,000-digit value can be stored once in the HPACK dynamic table and re-sent on each new stream for about one byte: 124 KB of traffic kept the server busy for 27.9 s.

This issue affects bandit: from 1.0.0-pre.7 before 1.14.0.

• Peter Ullrich reporter
• Mat Trudel remediation developer
• Jonatan Männchen / EEF analyst

• Quadratic bignum parsing of Content-Length and Host port values in Bandit
• EEF CNA record for CVE-2026-113436
• OSV record EEF-CVE-2026-113436
• Introducing commit e0c8c0c in mtrudel/bandit
• Fix commit 220b9df in mtrudel/bandit

• CWE-407 Inefficient Algorithmic Complexity CWE

• An unauthenticated client can make the server spend CPU time out of all proportion to the traffic it sends (27.9 s for 124 KB in the reporter's test). This affects any Bandit server reachable by untrusted clients over HTTP/1 or HTTP/2, with no special configuration.