---
id: CVE-2025-48994
aliases:
  - GHSA-6vx8-pcwv-xhf4
  - PYSEC-2026-1921
title: >-
  SignXML's signature verification with HMAC is vulnerable to an algorithm
  confusion attack
summary: >-
  SignXML's signature verification with HMAC is vulnerable to an algorithm
  confusion attack
severity: medium
vendor: signxml
product: signxml
ecosystem: pip
affected:
  - signxml < 4.0.4
patched:
  - signxml 4.0.4
published: '2025-06-05'
updated: '2026-07-07'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GHSA-6vx8-pcwv-xhf4'
references:
  - url: >-
      https://github.com/XML-Security/signxml/security/advisories/GHSA-6vx8-pcwv-xhf4
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2025-48994'
  - url: >-
      https://github.com/XML-Security/signxml/commit/e3c0c2b82a3329a65d917830657649c98b8c7600
  - url: 'https://github.com/XML-Security/signxml'
tags:
  - osv
  - pip
epss: 0.00219
epssPercentile: 0.11002
ingestedAt: '2026-07-08T18:25:46.538Z'
---

## Overview

When verifying signatures with X509 certificate validation turned off and HMAC shared secret set (`signxml.XMLVerifier.verify(require_x509=False, hmac_key=...`), prior versions of SignXML are vulnerable to a potential algorithm confusion attack. Unless the user explicitly limits the expected signature algorithms using the `signxml.XMLVerifier.verify(expect_config=...)` setting, an attacker may supply a signature unexpectedly signed with a key other than the provided HMAC key, using a different (asymmetric key) signature algorithm.

Starting with signxml 4.0.4, specifying `hmac_key` causes the set of accepted signature algorithms to be restricted to HMAC only, if not already restricted by the user.

## Affected packages

- `signxml < 4.0.4`

## Remediation

Upgrade to a patched release:

- `signxml 4.0.4`