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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 Red Hat
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

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. Rated CVSS 6.8 with high confidentiality and integrity impact; no public exploit or CISA KEV listing identified at time of analysis.

Technical ContextAI

librest is a GLib-based GNOME library for accessing RESTful web services, used by GNOME applications and GTK-based clients that implement OAuth 2.0 authorization flows. PKCE (Proof Key for Code Exchange, RFC 7636) is an OAuth 2.0 extension that prevents authorization code interception by binding the authorization request to a client-generated, cryptographically random 'code verifier.' The flaw (CWE-338: Use of Cryptographically Weak Pseudo-Random Number Generator) arises because librest calls GLib's GRand function - likely a Mersenne Twister or linear congruential generator - for this purpose. GRand's internal state is finite and its seed space is small (effectively 32-bit), meaning an attacker who observes sufficient PRNG output can recover the seed and reconstruct any future or concurrent verifier. The affected deployment context is confirmed via CPE cpe:2.3:a:red_hat:red_hat_enterprise_linux_10 and tracked upstream at gitlab.gnome.org/GNOME/librest/-/issues/25.

RemediationAI

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. The correct fix requires replacing GRand with a CSPRNG for code verifier generation - suitable alternatives include GLib's g_random_bytes() when backed by OS entropy, or direct use of /dev/urandom via GLib I/O. Until a patched release is available, organizations should monitor https://access.redhat.com/security/cve/CVE-2026-16615 and https://bugzilla.redhat.com/show_bug.cgi?id=2504432 for patch announcements. As a compensating control, applications initiating OAuth flows via librest can be configured to enforce short authorization code lifetimes on the authorization server side, reducing the window available to a seed-recovery attacker, though this does not eliminate the underlying weakness. Switching to an alternative OAuth client library with CSPRNG-based PKCE is the most reliable interim mitigation for high-sensitivity deployments.

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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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