CVE-2026-72889 Net::OAuth versions before 0.33 for Perl allow the sender to choose the signature algorithm in verify
Attackers can forge OAuth requests by choosing a weak signature algorithm, bypassing authentication checks in Net::OAuth Perl library.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-72889?
CVE-2026-72889 is a critical vulnerability, published on 19 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Which versions are affected by CVE-2026-72889?
How do I fix CVE-2026-72889?
Upgrade to a fixed version.
Is CVE-2026-72889 being exploited?
There is no known exploitation of CVE-2026-72889 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-72889, GHSA-c8rm-g5cm-4pf5, UBUNTU-CVE-2026-72889.