CVE-2025-48995: Signxml SignXML's Signature Verification With HMAC Vulnerability

MODERATE
Advisory Identifier: GHSA-gmhf-gg8w-jw42
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CWE-208
Published
Advisory Summary

CVE-2025-48995 is a MODERATE signxml's signature verification with hmac vulnerability (CWE-208: Observable Timing Discrepancy) affecting Signxml libraries in the PyPI ecosystem. The issue involves signxml's signature verification with hmac is vulnerable to a timing attack. Remediation is available by upgrading affected packages to version 4.0.4.

CVE-2025-48995 at a Glance

CVE Identifier CVE-2025-48995
GHSA Identifier GHSA-gmhf-gg8w-jw42
Severity MODERATE
CVSS v3.1 Base Score N/A
CWE Classification CWE-208: Observable Timing Discrepancy
Affected Product Signxml
Package Ecosystem PyPI
Published Date
Last Updated

How to Fix CVE-2025-48995

To remediate this vulnerability, upgrade all affected Signxml dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

signxml fixed: 4.0.4 
pip install signxml>=4.0.4
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

pip show signxml

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2025-48995, inspect your installed packages using pip:

pip show signxml

Analyze the terminal output to locate any version of Signxml in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 4.0.4), your application is affected.

Note: The pip show signxml command checks currently installed packages in your active Python environment.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-208: Observable Timing Discrepancy, where two separate operations in a product require different amounts of time to complete, in a way that is observable to an actor and reveals security-relevant information about the state of the product, such as whether a particular operation was successful or not. In Signxml, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

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 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.

CVE-2025-48995 Affected Signxml Versions

1 component(s)
Fixed Versions:
4.0.4
Product / Package Ecosystem Affected Versions Fixed Version
signxml
pypi/signxml
PyPI
< 4.0.4
4.0.4

References

GitHub Advisory / Wiki ADVISORY
https://github.com/XML-Security/signxml/security/advisories/GHSA-gmhf-gg8w-jw42
NVD — CVE-2025-48995 NVD
https://nvd.nist.gov/vuln/detail/CVE-2025-48995
Security Fix Commit FIX COMMIT
https://github.com/XML-Security/signxml/commit/1b501faaacf34cf978a52dbc6915ec11e27611cd
Signxml Source Repository REPOSITORY
https://github.com/XML-Security/signxml

Frequently Asked Questions

What is CVE-2025-48995?
CVE-2025-48995 is a security vulnerability in Signxml involving SignXML's signature verification with HMAC is vulnerable to a timing attack under CWE-208: Observable Timing Discrepancy.
Which Signxml versions are affected?
Affected versions include releases prior to 4.0.4 across affected packages: signxml.
What version fixes CVE-2025-48995?
Upgrading to 4.0.4 (or the latest patched release for your respective branch) resolves the vulnerability.
Is signxml affected?
Yes, signxml is affected in releases prior to 4.0.4. Upgrade your dependency to 4.0.4 or later.
What CWE is associated with CVE-2025-48995?
CVE-2025-48995 is classified under CWE-208: Observable Timing Discrepancy (Two separate operations in a product require different amounts of time to complete, in a way that is observable to an actor and reveals security-relevant information about the state of the product, such as whether a particular operation was successful or not.).
How can I check PyPI dependencies for CVE-2025-48995?
Run the dependency tree command: 'pip show signxml'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-gmhf-gg8w-jw42",
  "modified" : "2025-06-05T00:37:19Z",
  "published" : "2025-06-05T00:37:19Z",
  "aliases" : [ "CVE-2025-48995" ],
  "summary" : "SignXML's signature verification with HMAC is vulnerable to a timing attack",
  "details" : "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 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.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "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"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "signxml"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "4.0.4"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/XML-Security/signxml/security/advisories/GHSA-gmhf-gg8w-jw42"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2025-48995"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/XML-Security/signxml/commit/1b501faaacf34cf978a52dbc6915ec11e27611cd"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/XML-Security/signxml"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-208" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2025-06-05T00:37:19Z",
    "nvd_published_at" : "2025-06-02T17:15:41Z"
  }
}