Description

This release of Mbed TLS provides bug fixes, enhancements and new features. This release includes fixes for security issues.

Security Advisories

For full details, please see the following links:

https://tls.mbed.org/tech-updates/security-advisories/mbedtls-security-advisory-2021-07-1 https://tls.mbed.org/tech-updates/security-advisories/mbedtls-security-advisory-2021-07-2

Release Notes

API changes

• Update AEAD output size macros to bring them in line with the PSA Crypto API version 1.0 spec. This version of the spec parameterizes them on the key type used, as well as the key bit-size in the case of PSA_AEAD_TAG_LENGTH. The old versions of these macros were renamed and deprecated as follows:
  • PSA_AEAD_TAG_LENGTH -> PSA_AEAD_TAG_LENGTH_1_ARG
  • PSA_AEAD_ENCRYPT_OUTPUT_SIZE -> PSA_AEAD_ENCRYPT_OUTPUT_SIZE_2_ARG
  • PSA_AEAD_DECRYPT_OUTPUT_SIZE -> PSA_AEAD_DECRYPT_OUTPUT_SIZE_2_ARG
  • PSA_AEAD_UPDATE_OUTPUT_SIZE -> PSA_AEAD_UPDATE_OUTPUT_SIZE_2_ARG
  • PSA_AEAD_FINISH_OUTPUT_SIZE -> PSA_AEAD_FINISH_OUTPUT_SIZE_1_ARG
  • PSA_AEAD_VERIFY_OUTPUT_SIZE -> PSA_AEAD_VERIFY_OUTPUT_SIZE_1_ARG
• Implement one-shot cipher functions, psa_cipher_encrypt and psa_cipher_decrypt, according to the PSA Crypto API 1.0.0 specification.

Requirement changes

• The library now uses the %zu format specifier with the printf() family of functions, so requires a toolchain that supports it. This change does not affect the maintained LTS branches, so when contributing changes please bear this in mind and do not add them to backported code.

Features

• Add mbedtls_rsa_rsassa_pss_sign_ext() function allowing to generate a signature with a specific salt length. This function allows to validate test cases provided in the NIST's CAVP test suite. Contributed by Cédric Meuter in PR #3183.
• Added support for built-in driver keys through the PSA opaque crypto driver interface. Refer to the documentation of MBEDTLS_PSA_CRYPTO_BUILTIN_KEYS for more information.
• Implement psa_sign_message() and psa_verify_message().
• The new function mbedtls_mpi_random() generates a random value in a given range uniformly.
• Implement psa_mac_compute() and psa_mac_verify() as defined in the PSA Cryptograpy API 1.0.0 specification.
• MBEDTLS_ECP_MAX_BITS is now determined automatically from the configured curves and no longer needs to be configured explicitly to save RAM.

Security

• Fix a bias in the generation of finite-field Diffie-Hellman-Merkle (DHM) private keys and of blinding values for DHM and elliptic curves (ECP) computations. Reported by FlorianF89 in #4245.
• Fix a potential side channel vulnerability in ECDSA ephemeral key generation. An adversary who is capable of very precise timing measurements could learn partial information about the leading bits of the nonce used for the signature, allowing the recovery of the private key after observing a large number of signature operations. This completes a partial fix in Mbed TLS 2.20.0.
  • It was possible to configure MBEDTLS_ECP_MAX_BITS to a value that is too small, leading to buffer overflows in ECC operations. Fail the build in such a case.
  • An adversary with access to precise enough information about memory accesses (typically, an untrusted operating system attacking a secure enclave) could recover an RSA private key after observing the victim performing a single private-key operation. Found and reported by Zili KOU, Wenjian HE, Sharad Sinha, and Wei ZHANG.
  • An adversary with access to precise enough timing information (typically, a co-located process) could recover a Curve25519 or Curve448 static ECDH key after inputting a chosen public key and observing the victim performing the corresponding private-key operation. Found and reported by Leila Batina, Lukas Chmielewski, Björn Haase, Niels Samwel and Peter Schwabe.

Bugfix

• Add printf function attributes to mbedtls_debug_print_msg to ensure we get printf format specifier warnings.
• Fix premature fopen() call in mbedtls_entropy_write_seed_file which may lead to seed file corruption in the case where the path to the seed file is equal to MBEDTLS_PLATFORM_STD_NV_SEED_FILE. Contributed by Victor Krasnoshchok in #3616.
• PSA functions other than psa_open_key now return PSA_ERROR_INVALID_HANDLE rather than PSA_ERROR_DOES_NOT_EXIST for an invalid handle, bringing them in line with version 1.0.0 of the specification. Fix #4162.
• PSA functions creating a key now return PSA_ERROR_INVALID_ARGUMENT rather than PSA_ERROR_INVALID_HANDLE when the identifier specified for the key to create is not valid, bringing them in line with version 1.0.0 of the specification. Fix #4271.
• Fix some cases in the bignum module where the library constructed an unintended representation of the value 0 which was not processed correctly by some bignum operations. This could happen when mbedtls_mpi_read_string() was called on "-0", or when mbedtls_mpi_mul_mpi() and mbedtls_mpi_mul_int() was called with one of the arguments being negative and the other being 0. Fixes #4643.
• Fix a bug in ECDSA that would cause it to fail when the hash is all-bits zero. Fixes #1792
• Fix a compilation error when MBEDTLS_ECP_RANDOMIZE_MXZ_ALT is defined. Fixes #4217.
• Fix an incorrect error code when parsing a PKCS#8 private key.
• In a TLS client, enforce the Diffie-Hellman minimum parameter size set with mbedtls_ssl_conf_dhm_min_bitlen() precisely. Before, the minimum size was rounded down to the nearest multiple of 8.
• In library/net_sockets.c, _POSIX_C_SOURCE and _XOPEN_SOURCE are defined to specific values. If the code is used in a context where these are already defined, this can result in a compilation error. Instead, assume that if they are defined, the values will be adequate to build Mbed TLS.
• The cipher suite TLS-RSA-WITH-CAMELLIA-256-GCM-SHA384 was not available when SHA-1 was disabled and was offered when SHA-1 was enabled but SHA-384 was disabled. Fix the dependency. Fixes #4472.
• Do not offer SHA384 cipher suites when SHA-384 is disabled. Fixes #4499.
• With MBEDTLS_PSA_CRYPTO_C disabled, some functions were getting built nonetheless, resulting in undefined reference errors when building a shared library. Reported by Guillermo Garcia M. in #4411.
• Fix test suite code on platforms where int32_t is not int, such as Arm Cortex-M. Fixes #4530.
• Fix some issues affecting MBEDTLS_ARIA_ALT implementations: a misplaced directive in a header and a missing initialization in the self-test.
• Fix a missing initialization in the Camellia self-test, affecting MBEDTLS_CAMELLIA_ALT implementations.
• Restore the ability to configure PSA via Mbed TLS options to support RSA key pair operations but exclude RSA key generation. When MBEDTLS_GENPRIME is not defined PSA will no longer attempt to use mbedtls_rsa_gen_key(). Fixes #4512.
• Fix a regression introduced in 2.24.0 which broke (D)TLS CBC ciphersuites (when the encrypt-then-MAC extension is not in use) with some ALT implementations of the underlying hash (SHA-1, SHA-256, SHA-384), causing the affected side to wrongly reject valid messages. Fixes #4118.
• Remove outdated check-config.h check that prevented implementing the timing module on Mbed OS. Fixes #4633.
• Fix PSA_ALG_TLS12_PRF and PSA_ALG_TLS12_PSK_TO_MS being too permissive about missing inputs.
• Fix mbedtls_net_poll() and mbedtls_net_recv_timeout() often failing with MBEDTLS_ERR_NET_POLL_FAILED on Windows. Fixes #4465.
• Fix a resource leak in a test suite with an alternative AES implementation. Fixes #4176.
• Fix a crash in mbedtls_mpi_debug_mpi on a bignum having 0 limbs. This could notably be triggered by setting the TLS debug level to 3 or above and using a Montgomery curve for the key exchange. Reported by lhuang04 in #4578. Fixes #4608.
• psa_verify_hash() was relying on implementation-specific behavior of mbedtls_rsa_rsassa_pss_verify() and was causing failures in some _ALT implementations. This reliance is now removed. Fixes #3990.
• Disallow inputs of length different from the corresponding hash when signing or verifying with PSA_ALG_RSA_PSS (The PSA Crypto API mandates that PSA_ALG_RSA_PSS uses the same hash throughout the algorithm.)
• Fix a null pointer dereference when mbedtls_mpi_exp_mod() was called with A=0 represented with 0 limbs. Up to and including Mbed TLS 2.26, this bug could not be triggered by code that constructed A with one of the mbedtls_mpi_read_xxx functions (including in particular TLS code) since those always built an mpi object with at least one limb. Credit to OSS-Fuzz. Fixes #4641.
• Fix mbedtls_mpi_gcd(G,A,B) when the value of B is zero. This had no effect on Mbed TLS's internal use of mbedtls_mpi_gcd(), but may affect applications that call mbedtls_mpi_gcd() directly. Fixes #4642.
• The PSA API no longer allows the creation or destruction of keys with a read-only lifetime. The persistence level PSA_KEY_PERSISTENCE_READ_ONLY can now only be used as intended, for keys that cannot be modified through normal use of the API.
• When MBEDTLS_PSA_CRYPTO_SPM is enabled, crypto_spe.h was not included in all the right places. Include it from crypto_platform.h, which is the natural place. Fixes #4649.
• mbedtls_pk_sign() and mbedtls_pk_verify() and their extended and restartable variants now always honor the specified hash length if nonzero. Before, for RSA, hash_len was ignored in favor of the length of the specified hash algorithm.
• Fix which alert is sent in some cases to conform to the applicable RFC: on an invalid Finished message value, an invalid max_fragment_length extension, or an unsupported extension used by the server.
• Correct (change from 12 to 13 bytes) the value of the macro describing the maximum nonce length returned by psa_aead_generate_nonce().

Changes

• Add extra printf compiler warning flags to builds.
• Fix memsan build false positive in x509_crt.c with Clang 11
• Fix the setting of the read timeout in the DTLS sample programs.
• Remove the AES sample application programs/aes/aescrypt2 which shows bad cryptographic practice. Fix #1906.
• Alternative implementations of CMAC may now opt to not support 3DES as a CMAC block cipher, and still pass the CMAC self test.
• Remove configs/config-psa-crypto.h, which was identical to the default configuration except for having some extra cryptographic mechanisms enabled and for unintended differences. This configuration was primarily intended to demonstrate the PSA API, and lost most of its usefulness when MBEDTLS_PSA_CRYPTO_C became enabled by default.
• When building the test suites with GNU make, invoke python3 or python, not python2, which is no longer supported upstream. * When using session cache based session resumption on the server, double-check that custom session cache implementations return sessions which are consistent with the negotiated ciphersuite and compression method.
• Fix build failure on MinGW toolchain when __USE_MING_ANSI_STDIO is on. When that flag is on, standard GNU C printf format specifiers should be used.
• Reduce the default value of MBEDTLS_ECP_WINDOW_SIZE. This reduces RAM usage during ECC operations at a negligible performance cost.
• mbedtls_mpi_read_binary(), mbedtls_mpi_read_binary_le() and mbedtls_mpi_read_string() now construct an mbedtls_mpi object with 0 limbs when their input has length 0. Note that this is an implementation detail and can change at any time, so this change should be transparent, but it may result in mbedtls_mpi_write_binary() or mbedtls_mpi_write_string() now writing an empty string where it previously wrote one or more zero digits when operating from values constructed with an mpi_read function and some mpi operations.
• Implicitly add PSA_KEY_USAGE_SIGN_MESSAGE key usage policy flag when PSA_KEY_USAGE_SIGN_HASH flag is set and PSA_KEY_USAGE_VERIFY_MESSAGE flag when PSA_KEY_USAGE_VERIFY_HASH flag is set. This usage flag extension is also applied when loading a key from storage.

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:

2a07856e541f0e5f6eaee4f78018c52f25bd244ed76f9020dea54a8b02cac6ea mbedtls-2.27.0.tar.gz e580970a766fdaba2b70bcf3e69de34a67684e7f23a815b97f79771382c43651 mbedtls-2.27.0.zip