CVE-2020-36478: Release Mbed TLS 2.16.9 · Mbed-TLS/mbedtls

Description

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

Security

• Limit the size of calculations performed by mbedtls_mpi_exp_mod to MBEDTLS_MPI_MAX_SIZE to prevent a potential denial of service when generating Diffie-Hellman key pairs. Credit to OSS-Fuzz.
• A failure of the random generator was ignored in mbedtls_mpi_fill_random(), which is how most uses of randomization in asymmetric cryptography (including key generation, intermediate value randomization and blinding) are implemented. This could cause failures or the silent use of non-random values. A random generator can fail if it needs reseeding and cannot not obtain entropy, or due to an internal failure (which, for Mbed TLS’s own CTR_DRBG or HMAC_DRBG, can only happen due to a misconfiguration).
• Fix a compliance issue whereby we were not checking the tag on the algorithm parameters (only the size) when comparing the signature in the description part of the cert to the real signature. This meant that a NULL algorithm parameters entry would look identical to an array of REAL (size zero) to the library and thus the certificate would be considered valid. However, if the parameters do not match in any way then the certificate should be considered invalid, and indeed OpenSSL marks these certs as invalid when mbedtls did not. Many thanks to guidovranken who found this issue via differential fuzzing and reported it in #3629.
• Zeroising of local buffers and variables which are used for calculations in mbedtls_pkcs5_pbkdf2_hmac(), mbedtls_internal_sha*_process(), mbedtls_internal_md*_process() and mbedtls_internal_ripemd160_process() functions to erase sensitive data from memory. Reported by Johan Malmgren and Johan Uppman Bruce from Sectra.

Bugfix

• Fix an invalid (but nonzero) return code from mbedtls_pk_parse_subpubkey() when the input has trailing garbage. Fixes #2512.
• Fix rsa_prepare_blinding() to retry when the blinding value is not invertible (mod N), instead of returning MBEDTLS_ERR_RSA_RNG_FAILED. This addresses a regression but is rare in practice (approx. 1 in 2/sqrt(N)). Found by Synopsys Coverity, fix contributed by Peter Kolbus (Garmin). Fixes #3647.
• Fix the build when the macro _GNU_SOURCE is defined to a non-empty value. Fix #3432.
• Correct the default IV size for mbedtls_cipher_info_t structures using MBEDTLS_MODE_ECB to 0, since ECB mode ciphers don’t use IVs.
• Make arc4random_buf available on NetBSD and OpenBSD when _POSIX_C_SOURCE is defined. Fix contributed in #3571. Adopted for LTS branch 2.16 in #3602.
• Fix build failures on GCC 11. Fixes #3782.
• Fix a memory leak in mbedtls_mpi_sub_abs() when the result was negative (an error condition) and the second operand was aliased to the result.
• Fix a case in elliptic curve arithmetic where an out-of-memory condition could go undetected, resulting in an incorrect result.
• In CTR_DRBG and HMAC_DRBG, don’t reset the reseed interval in seed().
  Fixes #2927.
• In PEM writing functions, fill the trailing part of the buffer with null bytes. This guarantees that the corresponding parsing function can read the buffer back, which was the case for mbedtls_x509write_{crt,csr}_pem until this property was inadvertently broken in Mbed TLS 2.19.0. Fixes #3682.
• Fix a build failure that occurred with the MBEDTLS_AES_SETKEY_DEC_ALT option on. In this configuration key management methods that are required for MBEDTLS_CIPHER_MODE_XTS were excluded from the build and made it fail. Fixes #3818. Reported by John Stroebel.

Changes

• Reduce stack usage significantly during sliding window exponentiation. Reported in #3591 and fix contributed in #3592 by Daniel Otte.
• Remove the zeroization of a pointer variable in AES rounds. It was valid but spurious and misleading since it looked like a mistaken attempt to zeroize the pointed-to buffer. Reported by Antonio de la Piedra, CEA Leti, France.

Who should update

We recommend all affected 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:

fc17ff7d8c11d08f23ae2800a18269408ad2c24ea6bb8b9363e41a01c2425697  mbedtls-2.16.9.tar.gz
111300d0d307d738fb20596c358fda7129dfd5f5c682f055793262080ac50950  mbedtls-2.16.9.zip