sigstore-js: DSSE payloadType type-binding failure

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

sigstore-js provides JavaScript libraries for interacting with Sigstore services. Prior to 3.2.1, the preAuthEncoding function in @sigstore/core uses Node.js ascii encoding when converting the PAE string to bytes, allowing payloadType to be mutated after signing without invalidating the signature and breaking the type-binding guarantee that DSSE is designed to provide. This issue is fixed in version 3.2.1.

Source published

14 Jul 2026 20:36:28 UTC

Source modified

15 Jul 2026 12:54:55 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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CVSS 3.1 · 5.4 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:L

sigstore-js provides JavaScript libraries for interacting with Sigstore services. Prior to 3.2.1, the preAuthEncoding function in @sigstore/core uses Node.js ascii encoding when converting the PAE string to bytes, allowing payloadType to be mutated after signing without invalidating the signature and breaking the type-binding guarantee that DSSE is designed to provide. This issue is fixed in version 3.2.1.

Source published

14 Jul 2026 21:17:01 UTC

Source modified

24 Oct 2026 21:10:00 UTC

Observed here

25 Oct 2026 12:17:32 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · [email protected] · Secondary · 5.4 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:L

### 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 ```javascript 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 ```

Source published

26 Jun 2026 19:11:19 UTC

Source modified

10 Sep 2026 03:51:08 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

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

Publisher rating · MODERATE