Vulnerability · Published Oct 26, 2026 · Assigned by EEF
CVE-2026-113436Quadratic bignum parsing of Content-Length and Host port values in Bandit
High 8.7
In plain English
A high-severity security flaw in bandit from mtrudel. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.6% (higher than 49% of all known vulnerabilities).
Official description
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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu:22.04:LTS | bandit | no fix listed | UBUNTU-CVE-2026-113436 |
| Ubuntu:24.04:LTS | bandit | no fix listed | UBUNTU-CVE-2026-113436 |
| Ubuntu:26.04:LTS | bandit | no fix listed | UBUNTU-CVE-2026-113436 |
| Ubuntu:26.10 | bandit | no fix listed | UBUNTU-CVE-2026-113436 |
Affected products (as reported)
Weakness: CWE-407 · Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
References
- Quadratic bignum parsing of Content-Length and Host port values in Bandit vendor-advisory, related
- EEF CNA record for CVE-2026-113436 related
- OSV record EEF-CVE-2026-113436 related
- Introducing commit e0c8c0c in mtrudel/bandit related
- Fix commit 220b9df in mtrudel/bandit patch