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librest CVE-2026-16615

| EUVDEUVD-2026-47742 MEDIUM
Use of Cryptographically Weak Pseudo-Random Number Generator (PRNG) (CWE-338)
2026-07-22 redhat GHSA-223h-642r-2f6v
Authentication Bypass Red Hat Enterprise Linux 10 Suse
6.8
CVSS 3.1 · Vendor: redhat
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Severity by source

Vendor (redhat) PRIMARY
6.8 MEDIUM
AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N
vuln.today AI
6.8 MEDIUM

Network-reachable OAuth attack but requires PRNG seed recovery within auth window (AC:H) and active user flow (UI:R); full token access justifies C:H/I:H with no availability impact.

3.1 AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N
4.0 AV:N/AC:H/AT:P/PR:N/UI:A/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
SUSE
MEDIUM
qualitative
Red Hat
6.8 HIGH
qualitative

Primary rating from Vendor (redhat).

CVSS VectorVendor: redhat

CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N
Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None

Lifecycle Timeline

2
Analysis Generated
Jul 22, 2026 - 17:19 vuln.today
CVE Published
Jul 22, 2026 - 16:12 cve.org
MEDIUM 6.8

DescriptionCVE.org

A flaw was found in librest. The PKCE implementation for OAuth authorization uses the GRand function from the GLib API, a cryptographically insecure pseudo-random number generator. Because the generated "code verifier" lacks sufficient cryptographic entropy, a malicious actor can reverse-engineer the pseudo-random number generator (PRNG) seed to predict or reconstruct the code verifier string, allowing an attacker to bypass PKCE protections and successfully impersonate the client during the OAuth 2.0 authorization flow.

AnalysisAI

PKCE bypass in librest allows OAuth 2.0 client impersonation by exploiting a cryptographically weak pseudo-random number generator. The library's code verifier generation for PKCE (RFC 7636) uses GLib's GRand function - a non-cryptographic PRNG with a 32-bit seed space - rather than a CSPRNG, enabling a positioned attacker to recover the PRNG seed and reconstruct the code verifier to hijack the token exchange. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Recon
Position to observe OAuth flow
Delivery
User initiates librest OAuth authorization
Exploit
Capture code challenge derived from GRand output
Install
Brute-force 32-bit GRand PRNG seed
C2
Reconstruct code verifier
Execute
Submit verifier with intercepted auth code to token endpoint
Impact
Obtain OAuth access token as impersonated client
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Vulnerability AssessmentAI

Exploitation Exploitation requires that the target application uses librest's built-in PKCE implementation for OAuth 2.0 authorization flows - specifically the GRand-based code verifier generation path. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The CVSS 3.1 vector AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N scores 6.8, reflecting meaningful but non-trivial exploitation: the attacker must successfully recover GRand's PRNG seed (AC:H) within the bounded lifetime of an OAuth authorization code, and a legitimate user must first initiate the flow (UI:R). … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario An attacker positioned to monitor or interfere with a target user's OAuth authorization flow - for example, via a network vantage point or a malicious application on the same host - observes the code challenge derived from librest's GRand-generated code verifier. The attacker brute-forces or reconstructs the 32-bit GRand seed from observed outputs, predicts the code verifier, and submits it to the OAuth token endpoint alongside the intercepted authorization code, obtaining a valid access token as the legitimate client. …
Remediation No patched version of librest has been confirmed in available references; the fix is currently tracked as an upstream issue at https://gitlab.gnome.org/GNOME/librest/-/issues/25. … Detailed patch versions, workarounds, and compensating controls in full report.
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Vendor StatusVendor

SUSE

Severity: Moderate
Product Status
SUSE Liberty Linux 10 Fixed
SUSE Linux Enterprise Desktop 15 SP7 Affected
SUSE Linux Enterprise Desktop 15 SP7 Affected
SUSE Linux Enterprise High Performance Computing 15 SP7 Affected
SUSE Linux Enterprise Module for Desktop Applications 15 SP7 Affected

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CVE-2026-16615 vulnerability details – vuln.today
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