# CVE-2026-34871: Arm Mbed TLS Predictable Seed in PRNG on Linux

Source: https://junglewise.ai/threats/cve-2026-34871-arm-mbed-tls-predictable-seed-in-prng-on-linux  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-04-01. Updated: 2026-06-05  
License: CC BY 4.0 with a link back

CVE-2026-34871 · Severity: medium · CVSS 6.7 · Published 2026-04-01

Mbed TLS and TF-PSA-Crypto are cryptographic libraries used to secure data and communications, often in embedded devices. A vulnerability was found where the software might use a predictable source of randomness on Linux systems during early boot or installation. This could allow an attacker to predict security keys or bypass encryption, potentially leading to the exposure of sensitive data or unauthorized access to the device.

Technologies: [Arm Mbed Tls](https://junglewise.ai/threats/technologies/mbed-tls). Vendors: [Arm](https://junglewise.ai/threats/vendors/arm).

## Quick answers

**Is CVE-2026-34871 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-34871 being exploited in the wild.

**How severe is CVE-2026-34871?** Medium severity, with a CVSS score of 6.7, published 1 April 2026.

**Which products and versions are affected?** Arm Mbed Tls up to 3.6.5, 4.0.0.

**Is there a fix for CVE-2026-34871?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-34871 attacked?** It is attacked with local access, in a software library.

**Am I affected by CVE-2026-34871?** Check whether you run Arm Mbed Tls at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A predictable seed vulnerability exists in Mbed TLS (before 3.6.6 and 4.1.0) and TF-PSA-Crypto (before 1.1.0) due to an insecure fallback mechanism on Linux. When the getrandom() system call is unavailable—due to old kernels (pre-3.17), restricted environments, or toolchain limitations—the library falls back to reading from /dev/urandom. On systems without a hardware RNG or saved entropy files, /dev/urandom can return predictable data during early boot or OS installation. This allows for the generation of predictable cryptographic keys and may leak private keys if randomized ECDSA signatures are used. The fix involves transitioning the fallback from /dev/urandom to /dev/random, which blocks until sufficient entropy is available.

## Affected products

- Arm Mbed TLS up to 3.6.5, 4.0.0
- Arm TF-PSA-Crypto up to 1.0.0

## Timeline

- 2026-03-31: advisory: Vendor advisory published by Mbed TLS team
- 2026-04-01: disclosed: CVE-2026-34871 published

## References

- [https://mbed-tls.readthedocs.io/en/latest/security-advisories/](https://mbed-tls.readthedocs.io/en/latest/security-advisories/)
- [https://mbed-tls.readthedocs.io/en/latest/security-advisories/mbedtls-security-advisory-2026-03-dev-random/](https://mbed-tls.readthedocs.io/en/latest/security-advisories/mbedtls-security-advisory-2026-03-dev-random/)

## Related threats

- [Mbed TLS memory corruption via insecure deserialization of SSL context](https://junglewise.ai/threats/cve-2026-34877-mbed-tls-memory-corruption-via-insecure-deserialization-of-ssl)
- [Mbed TLS client impersonation in TLS 1.3 session resumption](https://junglewise.ai/threats/cve-2026-34873-mbed-tls-client-impersonation-in-tls-1-3-session-resumption)
- [In Mbed TLS through 4.0.0, there is a compiler-induced timing side channel (in RSA and CBC/ECB decryption) that only…](https://junglewise.ai/threats/cve-2025-66442-in-mbed-tls-through-4-0-0-there-is-a-compiler-induced-timing-side)
- [Arm Mbed TLS and TF-PSA-Crypto PRNG state cloning vulnerability](https://junglewise.ai/threats/cve-2026-25835-arm-mbed-tls-and-tf-psa-crypto-prng-state-cloning-vulnerability)
- [Mbed TLS out-of-bounds read in mbedtls_lms_import_public_key](https://junglewise.ai/threats/cve-2025-49601-mbed-tls-out-of-bounds-read-in-mbedtls-lms-import-public-key)