# CVE-2025-48994: SignXML's signature verification with HMAC is vulnerable to an algorithm confusion attack

> Attackers can bypass signature verification in SignXML by exploiting algorithm confusion when X509 validation is disabled and HMAC keys are used.

- **Severity:** Medium 6.9 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 2 Jun 2025
- **Updated:** 2 Jun 2025
- **Also known as:** DEBIAN-CVE-2025-48994, GHSA-6vx8-pcwv-xhf4, PYSEC-2026-1921, UBUNTU-CVE-2025-48994

## What is CVE-2025-48994?

CVE-2025-48994 is a medium-severity vulnerability in XML-Security signxml, published on 2 Jun 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

SignXML is an implementation of the W3C XML Signature standard in Python. When verifying signatures with X509 certificate validation turned off and HMAC shared secret set (`signxml.XMLVerifier.verify(require_x509=False, hmac_key=...`), versions of SignXML prior to 4.0.4 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.

Weakness: CWE-303 (Incorrect Implementation of Authentication Algorithm)

## Which versions are affected by CVE-2025-48994?

3 open source packages ship an affected version, including signxml.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `signxml` | PyPI | All versions | 4.0.4 |
| `signxml` | PyPI | All versions | 4.0.4 |
| `signxml` | PyPI | All versions | 4.0.4 |

## How do I fix CVE-2025-48994?

Upgrade signxml to 4.0.4 or later.

## Is CVE-2025-48994 being exploited?

There is no known exploitation of CVE-2025-48994 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-48994 and fix it if it is affected.

What it is: CVE-2025-48994 is a medium-severity vulnerability in XML-Security signxml, published on 2 Jun 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2025-48994 in the wild and no public exploit code.

Affected packages and fixed versions:
- signxml (PyPI): affected all versions; fixed in 4.0.4
- signxml (PyPI): affected all versions; fixed in 4.0.4
- signxml (PyPI): affected all versions; fixed in 4.0.4

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2025-48994/ (Markdown: https://insights.sbomify.com/CVE-2025-48994/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-48994
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-48994
- OSV: https://osv.dev/vulnerability/CVE-2025-48994

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-48994/
Summaries are generated and may contain mistakes; the official description above is the record.