Description

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

Default behavior changes

• In mbedtls_rsa_context objects, the ver field was formerly documented as always 0. It is now reserved for internal purposes and may take different values.

Security

• Fix a buffer overflow in mbedtls_mpi_sub_abs() when calculating |A| - |B| where |B| is larger than |A| and has more limbs (so the function should return MBEDTLS_ERR_MPI_NEGATIVE_VALUE). Only applications calling mbedtls_mpi_sub_abs() directly are affected: all calls inside the library were safe since this function is only called with |A| >= |B|. Reported by Guido Vranken in #4042.
• Fix an errorneous estimation for an internal buffer in mbedtls_pk_write_key_pem(). If MBEDTLS_MPI_MAX_SIZE is set to an odd value the function might fail to write a private RSA keys of the largest supported size. Found by Daniel Otte, reported in #4093 and fixed in #4094, backported in #4100.
• Fix a stack buffer overflow with mbedtls_net_poll() and mbedtls_net_recv_timeout() when given a file descriptor that is beyond FD_SETSIZE. Reported by FigBug in #4169.
• Guard against strong local side channel attack against base64 tables by making access aceess to them use constant flow code. (CVE-2021-24119)

Bugfix

• Fix an incorrect error code if an RSA private operation glitched.
• Fix a resource leak in CTR_DRBG and HMAC_DRBG when MBEDTLS_THREADING_C is enabled, on platforms where initializing a mutex allocates resources. This was a regression introduced in the previous release. Reported in #4017, #4045 and #4071.
• Ensure that calling mbedtls_rsa_free() or mbedtls_entropy_free() twice is safe. This happens for RSA when some Mbed TLS library functions fail. Such a double-free was not safe when MBEDTLS_THREADING_C was enabled on platforms where freeing a mutex twice is not safe.
• Fix a resource leak in a bad-arguments case of mbedtls_rsa_gen_key() when MBEDTLS_THREADING_C is enabled on platforms where initializing a mutex allocates resources.
• This change makes 'mbedtls_x509write_crt_set_basic_constraints' consistent with RFC 5280 4.2.1.9 which says: "Conforming CAs MUST include this extension in all CA certificates that contain public keys used to validate digital signatures on certificates and MUST mark the extension as critical in such certificates." Previous to this change, the extension was always marked as non-critical. This was fixed by #4044.

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:

96257bb03b30300b2f35f861ffe204ed957e9fd0329d80646fe57fc49f589b29 mbedtls-2.16.10.tar.gz 8a1537efd03dacdb0fc4bd6fddac0b0a49f91c229182268815e5980b9ffc555a mbedtls-2.16.10.zip