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9.8
CVE-2026-72887: Perl Net::OAuth::Client Downgrade to OAuth 1.0 Risk
CVE-2026-72887 · published 18 days ago
Summary
Net::OAuth::Client versions before 0.32 for Perl allow a service provider to quietly change the security level of OAuth 1.0a to OAuth 1.0, which can be exploited by attackers to take control of user accounts. This can happen if the service provider doesn't confirm the callback URL, and it's not something that can be prevented by the application. To protect your users, update to the latest version of Net::OAuth::Client.
What to do
The CVE record does not list a fixed version. Check the vendor's site or the advisory links below - a fix may already be released.
Affected software
| Ecosystem | Vendor | Product | Affected versions |
|---|---|---|---|
| Debian:14 | debian | libnet-oauth-perl | All versions |
| Debian:11 | debian | libnet-oauth-perl | All versions |
| Debian:12 | debian | libnet-oauth-perl | All versions |
| Debian:13 | debian | libnet-oauth-perl | All versions |
Original advisory text
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 ...
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.
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.
References
- https://datatracker.ietf.org/doc/html/rfc5849#section-2.1
- https://datatracker.ietf.org/doc/html/rfc5849#section-2.3
- https://security-tracker.debian.org/tracker/CVE-2026-72887 Vendor Advisory
- https://github.com/vurtdev/Net-OAuth/commit/fd505dac1988723ed96721657663f2e4ac73...
- https://github.com/vurtdev/Net-OAuth/security/advisories/GHSA-jh72-4qq2-8j6g
- https://metacpan.org/release/RRWO/Net-OAuth-0.32/changes
- http://www.openwall.com/lists/oss-security/2026/08/16/3
Severity
9.8
Critical
Exploitation
EPSS <1%
Type
CWE-757Selection of Less-Secure Algorithm During Negotiation ('Algorithm Downgrade')
Timeline
Published16 Aug 2026
Updated3 Sep 2026
First seen16 Aug 2026
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