What is the CVSS score of CVE-2026-48758?

CVE-2026-48758 has a CVSS 3.1 base score of 5.4 (Medium). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:L. EPSS exploitation probability: 0.3%.

Is there a patch available for CVE-2026-48758?

Yes, a patch is available for CVE-2026-48758. Update the affected software to the latest version immediately.

Node.js CVE-2026-48758

EUVD-2026-44501 MEDIUM

Improper Verification of Cryptographic Signature (CWE-347)

2026-06-26 https://github.com/sigstore/sigstore-js

GHSA-jfc7-64v2-mr8c

Node.js Jwt Attack Information Disclosure

5.4

CVSS 3.1 · Vendor: https://github.com/sigstore/sigstore-js

Severity by source

Vendor (https://github.com/sigstore/sigstore-js) PRIMARY

5.4 MEDIUM

AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:L

Primary rating from Vendor (https://github.com/sigstore/sigstore-js) · only source for this CVE.

CVSS VectorVendor: https://github.com/sigstore/sigstore-js

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

Attack Vector

Network

Attack Complexity

Low

Privileges Required

Low

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

Low

Availability

Low

Lifecycle Timeline

Source Code Evidence Fetched

Jun 26, 2026 - 19:52 vuln.today

Analysis Generated

Jun 26, 2026 - 19:52 vuln.today

Blast Radius

ecosystem impact

† from your stack dependencies † transitive graph · vuln.today resolves 4-path depth

3,610 npm packages depend on @sigstore/core (181 direct, 3,429 indirect)

Ecosystem-wide dependent count for version 3.2.1.

DescriptionCVE.org

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

AnalysisAI

Signature type-binding bypass in @sigstore/core (npm) allows an attacker who controls the payloadType field of a DSSE envelope to substitute every ASCII character with a Unicode variant whose low byte matches, producing PAE bytes identical to a legitimate signature and causing verification to pass for a mismatched content type. All versions up to and including 3.2.0 are affected; a working proof-of-concept is included in the GitHub security advisory GHSA-jfc7-64v2-mr8c. …