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GHSA-jfc7-64v2-mr8c
No affected components available
Impact
The preAuthEncoding function in @sigstore/core uses Node.js 'ascii' encoding when converting the PAE (Pre-Authentication Encoding) string to bytes. This allows payloadType to be mutated after signing without invalidating the signature, breaking the type-binding guarantee that DSSE is designed to provide.
In packages/core/src/dsse.ts, the PAE function builds a string containing payloadType and then encodes it with Buffer.from(prefix, 'ascii').
In Node.js, 'ascii' encoding for string-to-Buffer is equivalent to 'latin1', which truncates characters above U+00FF to their low byte. This means for any ASCII character, there exist Unicode characters (at U+01xx, U+02xx, etc.) that produce the identical encoded byte:
| Original | Codepoint | Mutant | Codepoint | Encoded byte |
|----------|-----------|--------|-----------|--------------|
| t | U+0074 | Ŵ | U+0174 | 0x74 |
| e | U+0065 | ť | U+0165 | 0x65 |
An attacker can substitute every character in payloadType with a Unicode variant whose low byte matches, producing identical PAE bytes and a passing signature verification.
Additionally, payloadType.length returns the JavaScript string length (UTF-16 code units) rather than the UTF-8 byte length required by the DSSE spec, though this is only a contributing factor for non-ASCII types.
Reproduction
const { preAuthEncoding } = require('@sigstore/core/dist/dsse.js');
const payload = Buffer.from('hello world');
const original = preAuthEncoding('text/plain', payload);
// U+01xx chars whose low bytes match the original ASCII chars
const mutant = preAuthEncoding('\u0174\u0165\u0178\u0174/\u0170\u016c\u0161\u0169\u016e', payload);
console.log('PAE bytes equal:', original.equals(mutant)); // true — should be false
The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker needs basic access or low-level privileges. No user interaction is needed for the attacker to exploit this vulnerability. The impact is confined to the system where the vulnerability exists. There is a low impact on the integrity of the data. There is a low impact on the availability of the system.
Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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