CVE-2026-72889

Deferred Deferred - Pending Action

Signature Forgery in Net::OAuth Perl Library

Publication date: 2026-08-19

Last updated on: 2026-08-26

Assigner: CPANSec

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.

CVSS Scores

EPSS Scores

Probability:
Percentile:

Meta Information

Published

2026-08-19

Last Modified

2026-08-26

Generated

2026-09-08

AI Q&A

2026-08-19

EPSS Evaluated

2026-09-07

NVD

CVE-2026-72889

EUVD

EUVD-2026-62347

Affected Vendors & Products

Vendor	Product	Version / Range
vurtdev	net_oauth	to 0.32 (inc)
vurtdev	net_oauth	0.31

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-757	A protocol or its implementation supports interaction between multiple actors and allows those actors to negotiate which algorithm should be used as a protection mechanism such as encryption or authentication, but it does not select the strongest algorithm that is available to both parties.
CWE-347	The product does not verify, or incorrectly verifies, the cryptographic signature for data.

Attack-Flow Graph

Executive Summary

This vulnerability in Net::OAuth versions before 0.33 allows an attacker to manipulate the signature verification process by choosing the algorithm used to verify requests. Normally, the server should control which algorithm is used, but here the attacker can specify it via the oauth_signature_method parameter. For deployments using RSA-SHA1, the server only holds the consumer's public key, but an attacker can force the use of HMAC-SHA1, which derives the key from consumer_secret and token_secret. Since RSA-SHA1 deployments use a placeholder for consumer_secret, this placeholder becomes the key, allowing forged requests without needing the private key.

Detection Guidance

Check if your system uses Net::OAuth versions before 0.33. Run: perl -MNet::OAuth -e 'print $Net::OAuth::VERSION' to verify the installed version. Inspect OAuth 1.0 requests for dynamic signature method selection in the oauth_signature_method parameter. Monitor for unexpected HMAC-SHA1 usage in RSA-SHA1 deployments.

Impact Analysis

If you use Net::OAuth versions before 0.33, an attacker could forge authenticated requests to your system by manipulating the signature method. This could allow unauthorized access to protected resources, data breaches, or impersonation of legitimate users. The impact is higher for systems using RSA-SHA1, as the attacker only needs to guess a placeholder key to forge requests.

Compliance Impact

This vulnerability could lead to unauthorized access to sensitive data, violating confidentiality requirements under GDPR and HIPAA. GDPR requires protecting personal data, and HIPAA mandates safeguards for protected health information. A breach due to this flaw could result in non-compliance, legal penalties, and reputational damage.

Mitigation Strategies

Upgrade Net::OAuth to version 0.33 or later. If upgrading is not possible, restrict allowed signature methods by setting allowed_signature_methods or @Net::OAuth::ALLOWED_SIGNATURE_METHODS to only RSA-SHA1 or HMAC-SHA256. Review OAuth 1.0 server configurations to ensure only secure signature methods are accepted.

Hi! I’m here to help you understand CVE-2026-72889. Ask me anything about the vulnerability, its impact, or mitigation strategies.

0/70