# CVE-2025-48995: SignXML's signature verification with HMAC is vulnerable to a timing attack

> Attackers can exploit timing differences to reconstruct HMAC keys in SignXML when X509 validation is disabled, compromising signature integrity.

- **Severity:** Medium 6.9 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/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-2025-48995, GHSA-gmhf-gg8w-jw42, PYSEC-2026-1922, UBUNTU-CVE-2025-48995

## What is CVE-2025-48995?

CVE-2025-48995 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 timing attack. The verifier may leak information about the correct HMAC when comparing it with the user supplied hash, allowing users to reconstruct the correct HMAC for any data.

Weakness: CWE-208 (Observable Timing Discrepancy)

## Which versions are affected by CVE-2025-48995?

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-2025-48995?

Upgrade signxml to 4.0.4 or later.

## Is CVE-2025-48995 being exploited?

There is no known exploitation of CVE-2025-48995 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-48995 and fix it if it is affected.

What it is: CVE-2025-48995 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-2025-48995 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-2025-48995/ (Markdown: https://insights.sbomify.com/CVE-2025-48995/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-48995
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-48995
- OSV: https://osv.dev/vulnerability/CVE-2025-48995

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-48995/
Summaries are generated and may contain mistakes; the official description above is the record.