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      <title>GHSA-q67f-28xg-22rw — Forge has signature forgery in Ed25519 due to missing S &gt; L check</title>
      <link>https://vulnerability.circl.lu/vuln/ghsa-q67f-28xg-22rw</link>
      <description>&lt;p&gt;&lt;strong&gt;Affected:&lt;/strong&gt; npm: node-forge&lt;/p&gt;
&lt;p&gt;## Summary
Ed25519 signature verification accepts forged non-canonical signatures where the scalar S is not reduced modulo the group order (`S &amp;gt;= L`). A valid signature and its `S + L` variant both verify in forge, while Node.js `crypto.verify` (OpenSSL-backed) rejects the `S + L` variant, [as defined by the specification](https://datatracker.ietf.org/doc/html/rfc8032#section-8.4). This class of signature malleability has been exploited in practice to bypass authentication and authorization logic (see [CVE-2026-25793](https://nvd.nist.gov/vuln/detail/CVE-2026-25793), [CVE-2022-35961](https://nvd.nist.gov/vuln/detail/CVE-2022-35961)). Applications relying on signature uniqueness (i.e., dedup by signature bytes, replay tracking, signed-object canonicalization checks) may be bypassed.&lt;/p&gt;
&lt;p&gt;## Impacted Deployments
**Tested commit:** `8e1d527fe8ec2670499068db783172d4fb9012e5`
**Affected versions:** tested on v1.3.3 (latest release) and all versions since Ed25519 was implemented.&lt;/p&gt;
&lt;p&gt;**Configuration assumptions:**
- Default forge Ed25519 verify API path (`ed25519.verify(...)`).&lt;/p&gt;
&lt;p&gt;## Root Cause
In `lib/ed25519.js`, `crypto_sign_open(...)` uses the signature&amp;#39;s last 32 bytes (`S`) directly in scalar multiplication:&lt;/p&gt;
&lt;p&gt;```javascript
scalarbase(q, sm.subarray(32));
```&lt;/p&gt;
&lt;p&gt;There is no prior check enforcing `S &amp;lt; L` (Ed25519 group order). As a result, equivalent scalar classes can pass verification, including a modified signature where `S := S + L (mod 2^256)` when that value remains non-canonical.…&lt;/p&gt;</description>
      <content:encoded>&lt;p&gt;&lt;strong&gt;Affected:&lt;/strong&gt; npm: node-forge&lt;/p&gt;
&lt;p&gt;## Summary
Ed25519 signature verification accepts forged non-canonical signatures where the scalar S is not reduced modulo the group order (`S &amp;gt;= L`). A valid signature and its `S + L` variant both verify in forge, while Node.js `crypto.verify` (OpenSSL-backed) rejects the `S + L` variant, [as defined by the specification](https://datatracker.ietf.org/doc/html/rfc8032#section-8.4). This class of signature malleability has been exploited in practice to bypass authentication and authorization logic (see [CVE-2026-25793](https://nvd.nist.gov/vuln/detail/CVE-2026-25793), [CVE-2022-35961](https://nvd.nist.gov/vuln/detail/CVE-2022-35961)). Applications relying on signature uniqueness (i.e., dedup by signature bytes, replay tracking, signed-object canonicalization checks) may be bypassed.&lt;/p&gt;
&lt;p&gt;## Impacted Deployments
**Tested commit:** `8e1d527fe8ec2670499068db783172d4fb9012e5`
**Affected versions:** tested on v1.3.3 (latest release) and all versions since Ed25519 was implemented.&lt;/p&gt;
&lt;p&gt;**Configuration assumptions:**
- Default forge Ed25519 verify API path (`ed25519.verify(...)`).&lt;/p&gt;
&lt;p&gt;## Root Cause
In `lib/ed25519.js`, `crypto_sign_open(...)` uses the signature&amp;#39;s last 32 bytes (`S`) directly in scalar multiplication:&lt;/p&gt;
&lt;p&gt;```javascript
scalarbase(q, sm.subarray(32));
```&lt;/p&gt;
&lt;p&gt;There is no prior check enforcing `S &amp;lt; L` (Ed25519 group order). As a result, equivalent scalar classes can pass verification, including a modified signature where `S := S + L (mod 2^256)` when that value remains non-canonical.…&lt;/p&gt;</content:encoded>
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