Description

This release of Mbed TLS provides bug fixes and minor enhancements. This release includes fixes for security issues.

Mbed TLS 2.28 is a long-time support branch. It will be supported with bug-fixes and security fixes until end of 2024.

Security Advisories

For full details, please see the following links:

• Buffer overread in TLS stream cipher suites

Release Notes

Features

• The documentation of mbedtls_ecp_group now describes the optimized representation of A for some curves. Fixes #8045.

Security

• Developers using mbedtls_pkcs5_pbes2() or mbedtls_pkcs12_pbe() should review the size of the output buffer passed to this function, and note that the output after decryption may include CBC padding. Consider moving to the new functions mbedtls_pkcs5_pbes2_ext() or mbedtls_pkcs12_pbe_ext() which checks for overflow of the output buffer and reports the actual length of the output.
• Improve padding calculations in CBC decryption, NIST key unwrapping and RSA OAEP decryption. With the previous implementation, some compilers (notably recent versions of Clang and IAR) could produce non-constant time code, which could allow a padding oracle attack if the attacker has access to precise timing measurements.
• Fix a buffer overread when parsing short TLS application data records in ARC4 or null-cipher cipher suites. Credit to OSS-Fuzz.

Bugfix

• Fix x509 certificate generation to conform to RFC 5480 / RFC 5758 when using ECC key. The certificate was rejected by some crypto frameworks. Fixes #2924.
• Fix some cases where mbedtls_mpi_mod_exp, RSA key construction or ECDSA signature can silently return an incorrect result in low memory conditions.
• Fix IAR compiler warnings. Fixes #7873, #4300.
• Fix an issue when parsing an otherName subject alternative name into a mbedtls_x509_san_other_name struct. The type-id of the otherName was not copied to the struct. This meant that the struct had incomplete information about the otherName SAN and contained uninitialized memory.
• Fix the detection of HardwareModuleName otherName SANs. These were being detected by comparing the wrong field and the check was erroneously inverted.
• Fix an error when MBEDTLS_ECDSA_SIGN_ALT is defined but not MBEDTLS_ECDSA_VERIFY_ALT, causing ecdsa verify to fail. Fixes #7498.
• Functions in the ssl_cache module now return a negative MBEDTLS_ERR_xxx error code on failure. Before, they returned 1 to indicate failure in some cases involving a missing entry or a full cache.

Changes

• In configurations with ARIA or Camellia but not AES, the value of MBEDTLS_CIPHER_BLKSIZE_MAX was 8, rather than 16 as the name might suggest. This did not affect any library code, because this macro was only used in relation with CMAC which does not support these ciphers. Its value is now 16 if ARIA or Camellia are present. This may affect application code that uses this macro.

Who should update

We recommend all users should update to take advantage of the bug fixes contained in this release at an appropriate point in their development lifecycle.

Checksum

The SHA256 hashes for the archives are: dbd42a11c26143aa8de1c07fd6ec6765395e86b06f583f051cfa60e8f0b23125 mbedtls-2.28.5.tar.gz d3a6c0a9746ccae0e36ab914064ce37b0e2d92ccca909e4fd5f8015b51f34456 mbedtls-2.28.5.zip