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.
Net::OAuth::Client allows silent OAuth 1.0a downgrade, enabling session fixation attacks that link victim accounts to attacker-controlled sessions.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-72887?
CVE-2026-72887 is a critical vulnerability, published on 16 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-757
Which versions are affected by CVE-2026-72887?
How do I fix CVE-2026-72887?
Upgrade to a fixed version.
Is CVE-2026-72887 being exploited?
There is no known exploitation of CVE-2026-72887 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-72887, GHSA-jh72-4qq2-8j6g, UBUNTU-CVE-2026-72887.