CVE-2026-25835 Overview
CVE-2026-25835 is an Insecure Random Number Generation vulnerability affecting Mbed TLS before version 3.6.6 and TF-PSA-Crypto before version 1.1.0. The vulnerability stems from improper handling of seeds in the Pseudo-Random Number Generator (PRNG), which can lead to predictable random number generation and potentially compromise cryptographic operations that rely on secure randomness.
Critical Impact
Improper PRNG seed handling can result in cryptographic weaknesses, allowing attackers with local access to potentially predict random values used in key generation, session tokens, and other security-critical operations.
Affected Products
- Mbed TLS versions prior to 3.6.6
- TF-PSA-Crypto versions prior to 1.1.0
Discovery Timeline
- 2026-04-01 - CVE CVE-2026-25835 published to NVD
- 2026-04-01 - Last updated in NVD database
Technical Details for CVE-2026-25835
Vulnerability Analysis
This vulnerability is classified under CWE-335 (Incorrect Usage of Seeds in Pseudo-Random Number Generator). The flaw occurs when the PRNG implementation misuses seed values, potentially leading to a condition known as "RNG cloning" where multiple instances of the random number generator could produce identical or predictable output sequences.
In cryptographic libraries like Mbed TLS, the PRNG is fundamental to generating secure keys, initialization vectors, nonces, and other security-critical random data. When the seeding mechanism is improperly implemented, it can allow attackers with local access to reconstruct the internal state of the PRNG or predict future outputs.
The vulnerability requires local access to exploit, meaning an attacker would need to have some level of access to the system running the affected software. However, no user interaction is required to trigger the vulnerability, and successful exploitation could lead to high confidentiality and integrity impacts.
Root Cause
The root cause lies in the misuse of seeds within the PRNG implementation. Specifically, the vulnerability relates to how Mbed TLS handles the seeding process for its random number generator. This improper seed handling can result in scenarios where the randomness of generated values is compromised, as detailed in the Mbed TLS Advisory 2026-03: RNG Cloning.
Attack Vector
The attack vector is local, requiring an attacker to have access to the target system. Exploitation does not require elevated privileges or user interaction. An attacker could potentially:
- Observe or influence the seeding process of the PRNG
- Clone the internal state of the random number generator
- Predict future random values generated by the affected library
- Compromise cryptographic operations that depend on the PRNG output
The vulnerability affects the confidentiality and integrity of systems relying on Mbed TLS for cryptographic operations. For detailed technical information, refer to the Mbed TLS Security Advisories page.
Detection Methods for CVE-2026-25835
Indicators of Compromise
- Unexpected patterns or repetition in random values generated by applications using Mbed TLS
- Cryptographic key collisions or duplicate session identifiers in TLS communications
- Applications using Mbed TLS versions earlier than 3.6.6 or TF-PSA-Crypto versions earlier than 1.1.0
- Evidence of local access attempts targeting cryptographic subsystems
Detection Strategies
- Audit installed versions of Mbed TLS and TF-PSA-Crypto across all systems and containers
- Monitor for applications linked against vulnerable library versions using software composition analysis tools
- Implement entropy quality monitoring for critical cryptographic operations
- Review application logs for any anomalies in cryptographic function behavior
Monitoring Recommendations
- Deploy software bill of materials (SBOM) monitoring to track vulnerable library usage
- Implement file integrity monitoring on Mbed TLS library files
- Configure alerting for any system-level access to cryptographic entropy sources
- Monitor for unusual process behavior in applications using the affected libraries
How to Mitigate CVE-2026-25835
Immediate Actions Required
- Upgrade Mbed TLS to version 3.6.6 or later immediately
- Upgrade TF-PSA-Crypto to version 1.1.0 or later
- Identify all applications and systems using vulnerable versions of the affected libraries
- Regenerate cryptographic keys and certificates that may have been generated using the vulnerable PRNG
- Review any sensitive cryptographic material created with affected versions
Patch Information
Security patches are available from the Mbed TLS project. Organizations should update to Mbed TLS 3.6.6 or later, or TF-PSA-Crypto 1.1.0 or later. Detailed patching guidance is available in the Mbed TLS Advisory 2026-03: RNG Cloning.
Workarounds
- Restrict local access to systems running vulnerable versions of Mbed TLS until patching is complete
- Consider using additional entropy sources to supplement the PRNG where possible
- Implement defense-in-depth measures to limit the impact of potential cryptographic weaknesses
- Monitor cryptographic operations for anomalies until the patch can be applied
# Check Mbed TLS version
# For systems with pkg-config:
pkg-config --modversion mbedtls
# Verify library version in source
grep -r "MBEDTLS_VERSION_STRING" /path/to/mbedtls/include/
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
