AIKIDO-2026-223454
Mbed-TLS.mbedtls is vulnerable to Observable Timing Discrepancy
40
Medium Risk
This Affects:
Mbed-TLS.mbedtlsTL;DR
Mbed TLS removes PKCS#7 padding after block cipher decryption by first checking that the final byte is within a valid range and returning early when it is not. This early exit creates a timing side channel that behaves as a padding oracle. An attacker with a decryption oracle and timing measurements can recover the last byte of each block, and often the full plaintext when part of it is under their control. The fix makes the padding check run in constant time.
Who does this affect?
You are affected if you are using a version that falls within the vulnerable range and your application decrypts untrusted ciphertext using the PKCS#7 padding mode.
Background info
Mbed-TLS.mbedtls is vulnerable to Observable Timing Discrepancy in versions 3.6.1 - 3.6.3.
How to fix this
Upgrade the Mbed-TLS.mbedtls library to the patch version.
Links
GitHub Release
Other
github.com/Mbed-TLS/mbedtls-docs/blob/main/security-advisories/mbedtls-security-advisory-2025-06-5.md
mbed-tls.readthedocs.io/en/latest/tech-updates/security-advisories/
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SOC 2Compliant
ISO 27001Compliant