CVE-2026-33894: Forge Forged Signature Vulnerability (<1.4.0)

CVE-2026-33894 allows attackers to forge RSASSA PKCS#1 v1.5 signatures when using low public exponent keys (e=3) within the Forge library. This vulnerability stems from the library's flawed signature verification process, which fails to adequately validate the ASN structure. An attacker can craft malicious signatures by strategically inserting “garbage” bytes within the ASN structure, specifically targeting an addition field. This manipulation allows the forged signature to bypass verification, effectively mimicking a legitimate signature. The attack leverages a Bleichenbacher-style forgery technique, similar to CVE-2022-24771, but with a subtle difference in how the malicious bytes are introduced. Successful exploitation could lead to unauthorized transactions, data manipulation, or impersonation, depending on the application utilizing Forge for signature verification. The blast radius extends to any system relying on Forge for secure communication and authentication where RSASSA PKCS#1 v1.5 signatures with a public exponent of 3 are used. Sensitive data, such as financial records, user credentials, or critical system configurations, could be at risk if the forged signature is accepted as valid. The ability to forge signatures undermines the integrity of the entire system relying on the signature verification process.

1. Reserved2026-03-24
2. Published2026-03-26
3. Modified2026-03-31
4. EPSS updated2026-04-04

The primary mitigation for CVE-2026-33894 is to upgrade to Forge version 1.4.0 or later, which includes the necessary fixes to properly validate signatures and prevent the forgery. If upgrading is not immediately feasible, consider disabling the use of RSASSA PKCS#1 v1.5 signatures with a public exponent of 3. Alternatively, implement stricter input validation on the ASN structure to detect and reject malformed signatures. This workaround, however, is less robust than upgrading and requires careful implementation to avoid introducing new vulnerabilities. Ensure that all signature verification logic is thoroughly reviewed and tested after implementing any workaround. Prioritize the upgrade to version 1.4.0 as soon as possible, as it provides the most comprehensive and reliable protection against this vulnerability. After upgrading, perform thorough testing to confirm that the fix has been successfully applied and that the system functions as expected. Verification of the upgrade should include testing with known malicious signature samples to ensure the vulnerability is completely resolved.