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Node.js CVE-2026-48758

| EUVDEUVD-2026-44501 MEDIUM
Improper Verification of Cryptographic Signature (CWE-347)
2026-06-26 https://github.com/sigstore/sigstore-js GHSA-jfc7-64v2-mr8c
Information Disclosure Node.js Jwt Attack
5.4
CVSS 3.1 · Vendor: https://github.com/sigstore/sigstore-js
View

Vulnerability Assessment

Weakness
CWE
CWE-347
OWASP Top 10:2025
A04:2025 - Cryptographic Failures
ASVS 5.0
V11 - Cryptography Signature verification
This Month Plan within 30 days. Why: MEDIUM severity (CVSS 4.0-6.9).
Patch available 0.3% exploitation probability (EPSS)

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AnalysisAIv1 – Jun 26, 2026

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. The vulnerability is not confirmed in the CISA KEV catalog, but exploit code is publicly available, making exploitation straightforward for any attacker positioned to craft or relay DSSE envelopes.

Affected VersionsENISA

sigstore-js < 3.2.1

Affected Packages

npm @sigstore/core fix: 3.2.1
euvd sigstore_js fix: 3.2.1

Source: OSV (Open Source Vulnerabilities)

Affects your stack

Affects 2 packages in npm, euvd

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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
SUSE MEDIUM
Red Hat 5.4 MEDIUM

Primary rating from Vendor (https://github.com/sigstore/sigstore-js).

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

Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
Low

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:

OriginalCodepointMutantCodepointEncoded byte
tU+0074ŴU+01740x74
eU+0065ťU+01650x65

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

Threat Intelligence Overview

EPSS Score
0.3%
Top 82% exploitable
Threat Intel
1
1 source
Data Quality
6 sources
Confidence: High
EUVD NVD CVE.org EPSS GHSA Vendor GitHub

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue
Severity MEDIUM
CISA KEV No
Public POC No
EPSS 0.3%
Patch available Yes
Active threat No
Deciding rule
MEDIUM severity (CVSS 4.0-6.9)
What every action level means
Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.
Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.
This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.
This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.
Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived
Scheduled
Exploitation· derived
None
System Exposure· derived
Open
Automatable· derived
No
Human Impact· derived
Medium

Priority Score

27
Low Medium High Critical
KEV: 0
EPSS: 0
CVSS: +27
PoC: 0
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Attack Technique

Information Disclosure MEDIUM

Information disclosure occurs when an application unintentionally exposes sensitive data that aids attackers in reconnaissance or directly compromises security.

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Vendor StatusVendor

SUSE

Severity: Moderate
Product Status
SUSE Linux Enterprise High Performance Computing 12 Not-Affected
SUSE Linux Enterprise High Performance Computing 15 SP7 Not-Affected
SUSE Linux Enterprise High Performance Computing 15 SP7 Not-Affected
SUSE Linux Enterprise Module for Web and Scripting 15 SP7 Not-Affected
SUSE Linux Enterprise Module for Web and Scripting 15 SP7 Not-Affected

References

Advisories & patches
ADVISORY https://github.com/sigstore/sigstore-js/security/advisories/GHSA-jfc7-64v2-mr8c REF https://github.com/advisories/GHSA-jfc7-64v2-mr8c REF https://github.com/sigstore/sigstore-js/commit/b5aa4f1f8d2db0a9dfa6430fb114d9c2f1c304f7 REF https://github.com/sigstore/sigstore-js/pull/1657 REF https://github.com/sigstore/sigstore-js/releases/tag/%40sigstore%2Fcore%403.2.1

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