---
id: "CVE-2026-113877"
kind: "vulnerability"
aliases: ["CVE-2026-113877"]
title: "Perl HTTP::Headers::ActionPack: Accept-Language header causes CPU exhaustion"
severity: "high"
cvss: null
epss: 0.00325
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["http-headers", "package", "perl", "web-apps"]
not_affected_if: ["does-not-use-actionpack", "no-untrusted-accept-language"]
published_at: "2026-10-23T21:17:21+00:00"
first_seen_at: "2026-10-23T21:57:34+00:00"
updated_at: "2026-10-25T12:38:50+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-113877", "first_seen_at": "2026-10-23T21:57:34+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2026-113877", "first_seen_at": "2026-10-25T12:38:50+00:00"}]
---

# Perl HTTP::Headers::ActionPack: Accept-Language header causes CPU exhaustion

HTTP::Headers::ActionPack before 0.10 interpolates Accept-Language ranges into a regular expression without escaping, so a crafted header makes the regex engine backtrack for seconds. A remote attacker can exhaust CPU or make choose_language die in any application that passes it an untrusted Accept-Language header.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check the installed version: `perl -MHTTP::Headers::ActionPack -e 'print $HTTP::Headers::ActionPack::VERSION'` or `cpanm --info HTTP::Headers::ActionPack`
- Search dependency manifests and lock files (cpanfile, cpanfile.snapshot, Makefile.PL) for HTTP::Headers::ActionPack
- Check whether application code calls choose_language on request headers

## Fix

- Upgrade HTTP::Headers::ActionPack to `0.10` or later
- Until upgraded, validate or limit Accept-Language header length and content before calling choose_language

## Timeline

- 2026-10-23T21:57:34+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-113877
- 2026-10-25T12:38:50+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2026-113877

## From the sources

HTTP::Headers::ActionPack versions before 0.10 for Perl allow CPU exhaustion via Accept-Language ranges matched as regular expressions.

_language_match interpolates each Accept-Language range into the pattern `/^$range\-/i` without escaping it, so regular expression syntax in the header reaches the regex engine. A 12-byte range such as `(a?|b?){26}z` backtracks for seconds, and each increment of the quantifier doubles the time. An invalid range such as `(` fails to compile.

A remote attacker can exhaust CPU, or make choose_language die, in any application that passes an untrusted Accept-Language header to it.

---

_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_