Forge: Certificate signature verified with the issuer's RSA signature scheme

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Forge (also called node-forge) is a native implementation of Transport Layer Security in JavaScript. Prior to 1.4.1, the affected implementation used certificate.verify(child), _verifySignature(), lib/x509.js to process the relevant input or security decision. node-forge selected RSA padding and RSASSA-PSS parameters from the issuer certificate rather than the child certificate being verified. A child labeled as RSASSA-PSS could therefore be accepted with a PKCS#1 v1.5 signature when the issuer used PKCS#1 v1.5. The signature still had to be produced with the trusted issuer's private key, so this did not permit certificate identity forgery, but it could bypass policies that require a declared signature scheme. This issue is fixed in version 1.4.1.

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29 Oct 2026 18:33:46 UTC

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3 Nov 2026 16:17:21 UTC

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3 Nov 2026 17:57:17 UTC

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CVSS 3.1 · 3.7 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N

Forge (also called node-forge) is a native implementation of Transport Layer Security in JavaScript. Prior to 1.4.1, the affected implementation used certificate.verify(child), _verifySignature(), lib/x509.js to process the relevant input or security decision. node-forge selected RSA padding and RSASSA-PSS parameters from the issuer certificate rather than the child certificate being verified. A child labeled as RSASSA-PSS could therefore be accepted with a PKCS#1 v1.5 signature when the issuer used PKCS#1 v1.5. The signature still had to be produced with the trusted issuer's private key, so this did not permit certificate identity forgery, but it could bypass policies that require a declared signature scheme. This issue is fixed in version 1.4.1.

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Oct 29, 2026, 6:33:46 PM (timezone not stated)

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Nov 3, 2026, 4:17:21 PM (timezone not stated)

Saved here

14 Nov 2026 17:37:47 UTC

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ENISA EUVD · source terms and attribution apply

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EUVD CVSS 3.1 · 3.7 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N

Forge (also called node-forge) is a native implementation of Transport Layer Security in JavaScript. Prior to 1.4.1, the affected implementation used certificate.verify(child), _verifySignature(), lib/x509.js to process the relevant input or security decision. node-forge selected RSA padding and RSASSA-PSS parameters from the issuer certificate rather than the child certificate being verified. A child labeled as RSASSA-PSS could therefore be accepted with a PKCS#1 v1.5 signature when the issuer used PKCS#1 v1.5. The signature still had to be produced with the trusted issuer's private key, so this did not permit certificate identity forgery, but it could bypass policies that require a declared signature scheme. This issue is fixed in version 1.4.1.

Source published

29 Oct 2026 19:17:19 UTC

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4 Nov 2026 14:57:16 UTC

Saved here

10 Nov 2026 16:25:21 UTC

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CVSS 3.1 · [email protected] · Secondary · 3.7 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N

CVSS 3.1 · [email protected] · Primary · 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

### Summary When verifying a certificate, node-forge chose the RSA padding scheme (PKCS#1 v1.5 or RSASSA-PSS) and PSS parameters from the issuer certificate's own signature algorithm instead of the certificate being verified. A certificate labeled as signed with RSASSA-PSS could pass `verifyCertificateChain()` with a PKCS#1 v1.5 signature. Fixed in node-forge 1.4.1. ### Details `certificate.verify(child)` in `lib/x509.js` hashes the child's TBSCertificate with the digest of the child's signature algorithm, then calls `_verifySignature()` with the issuer certificate. `_verifySignature()` selected the padding scheme from that certificate's `signatureOid` and `signatureParameters`, so the child was verified with the issuer's own scheme rather than the one the child declares. As a result, a child certificate whose signature algorithm says RSASSA-PSS was accepted with a PKCS#1 v1.5 signature when the issuer itself was signed with PKCS#1 v1.5. The outer `signatureAlgorithm` field of a certificate is not covered by the signature, so an existing PKCS#1 v1.5 (SHA-256) certificate can be relabeled as RSASSA-PSS and still pass verification. The signature itself must still be made with the issuer's private key over the certificate's contents; no certificate can be forged. The same cause made correctly signed chains fail: a PKCS#1 v1.5 certificate issued by an RSASSA-PSS-signed certificate, or the reverse, was rejected. The fix verifies with the child certificate's signature scheme and parameters and the issuer's public key. ### Patches Fixed in node-forge 1.4.1. Certificate signatures are verified with the scheme of the certificate's own signature algorithm. ### Workarounds Applications that make decisions based on a certificate's signature algorithm can verify the signature themselves with that algorithm's scheme and the issuer's public key. ### References - https://www.rfc-editor.org/rfc/rfc4055#section-3 (RSASSA-PSS signature algorithm in certificates) - https://www.rfc-editor.org/rfc/rfc5280#section-4.1.1.2 (Certificate signatureAlgorithm) - https://cwe.mitre.org/data/definitions/347.html (CWE-347: Improper Verification of Cryptographic Signature) ### Severity CVSS 3.1: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N (3.7, Low) CVSS 4.0 (informational): CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N (6.3) CVSS 4.0 rates this Moderate because its integrity weighting is higher; the severity rating follows CVSS 3.1. ### Credits Reported by Brian Lee (@hibrian827, Georgia Tech SSLab, Team Atlanta), who also suggested the fix. ### Proof of concept Create a CA certificate signed with sha256WithRSAEncryption, and a leaf certificate whose signature algorithm fields (outer and in the TBSCertificate) are RSASSA-PSS with SHA-256/MGF1-SHA-256/salt 32, but sign the leaf's TBSCertificate with the CA key using PKCS#1 v1.5 (`caKey.sign(sha256)`). On 1.4.0, `forge.pki.verifyCertificateChain(forge.pki.createCaStore([ca]), [leaf])` returns `true`, although verifying the leaf's signature with RSASSA-PSS fails. On 1.4.1 it throws "Certificate signature is invalid.". No private key is needed for the same result: take any certificate signed by the CA with sha256WithRSAEncryption and replace only its outer signatureAlgorithm (outside the signed TBSCertificate) with the RSASSA-PSS identifier above. On 1.4.0 it still verifies and reports `signatureOid` as RSASSA-PSS; on 1.4.1 it is rejected. Regression tests are in tests/unit/x509.js ("signature scheme of the child certificate"). ### Impact Applications that rely on a certificate's declared signature algorithm, for example a policy that only accepts RSASSA-PSS-signed certificates, can be given a certificate labeled RSASSA-PSS whose signature was verified as PKCS#1 v1.5. The certificate must still have been signed by the trusted issuer's key, so the identity it certifies cannot be forged. There is no confidentiality or availability impact.

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10 Nov 2026 15:57:48 UTC

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10 Nov 2026 16:15:04 UTC

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10 Nov 2026 16:21:51 UTC

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GitHub Advisory Database · CC-BY-4.0

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CVSS_V3 · CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N

Publisher rating · LOW