---
id: "CVE-2026-120635"
kind: "vulnerability"
aliases: ["CVE-2026-120635"]
title: "Perl CGI: multipart parser lets form fields slip past WAFs"
severity: "medium"
cvss: null
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["cgi", "package", "perl", "waf", "web-apps"]
not_affected_if: ["no-multipart-forms", "no-waf-or-proxy-filtering"]
published_at: "2026-11-04T00:17:24+00:00"
first_seen_at: "2026-11-04T00:46:16+00:00"
updated_at: "2026-11-04T00:48:22+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-120635", "first_seen_at": "2026-11-04T00:46:16+00:00"}]
---

# Perl CGI: multipart parser lets form fields slip past WAFs

The Perl CGI module before 5.00 parses multipart form data differently from the HTTP standards, so a crafted request can hide form fields from a proxy or web application firewall. An attacker can use this to get past filtering that checks request bodies, and the exact impact on a given app depends on what that filtering protects.

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

## How to check

- Check the installed CGI module version with `perl -MCGI -e 'print $CGI::VERSION'`
- Look for Perl CGI in application dependencies (cpanfile, Makefile.PL, or cpan list output)

## Fix

- Perl CGI: move to `5.00` or later (per the advisory's stated range; the linked patch pages were not read)

## Timeline

- 2026-11-04T00:46:16+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-120635

## Documents

- [fix] Patch: github.com https://github.com/leejo/CGI.pm/commit/cbf04979f9974458ac223793bbd9d0b6a772aa66.patch
- [fix] Patch: github.com https://github.com/leejo/CGI.pm/commit/e0ef8f4248c6ae3025749040d8595d206b6a1b49.patch
- [fix] Patch: github.com https://github.com/leejo/CGI.pm/commit/f719fc08e8756708bcd4f1e357d5c0f8702f85dd.patch
- [fix] Patch: github.com https://github.com/leejo/CGI.pm/commit/fe9516804d59a3774e280c15dbb7072fbd0ba5f1.patch

## From the sources

CGI versions before 5.00 for Perl allow form fields to be smuggled past proxies and WAFs via multipart parsing that differs from the RFCs.

The multipart/form-data parser matches the boundary anywhere rather than at the start of a line, uses the boundary without its leading -- for some client-supplied User-Agent values, finds the Content-Disposition name and filename inside the quoted values of other parameters, and corrupts parts when the boundary nears the 4096-byte read size.

---

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