mbedTLS v2.24.0 Release Notes

Release Date: 2020-09-01 // over 1 year ago
  • Description

    🚀 This release of Mbed TLS provides bug fixes and minor enhancements. This release includes fixes for security issues and the most notable of them are described in more detail in the security advisories.

    API changes

    • In the PSA API, rename the types of elliptic curve and Diffie-Hellman group families to psa_ecc_family_t and psa_dh_family_t, in line with the PSA Crypto API specification version 1.0.0. Rename associated macros as well:
      PSA_ECC_CURVE_xxx renamed to PSA_ECC_FAMILY_xxx
      PSA_DH_GROUP_xxx renamed to PSA_DH_FAMILY_xxx

    0️⃣ Default behavior changes

    • Stop storing persistent information about externally stored keys created through PSA Crypto with a volatile lifetime. Reported in #3288 and contributed by Steven Cooreman in #3382.

    🔋 Features

    • The new function mbedtls_ecp_write_key() exports private ECC keys back to a byte buffer. It is the inverse of the existing mbedtls_ecp_read_key().
    • Support building on e2k (Elbrus) architecture: correctly enable -Wformat-signedness, and fix the code that causes signed-one-bit-field and sign-compare warnings. Contributed by makise-homura (Igor Molchanov) [email protected].

    🔒 Security

    • Fix a vulnerability in the verification of X.509 certificates when matching the expected common name (the cn argument of mbedtls_x509_crt_verify()) with the actual certificate name: when the subjecAltName extension is present, the expected name was compared to any name in that extension regardless of its type. This means that an attacker could for example impersonate a 4-bytes or 16-byte domain by getting a certificate for the corresponding IPv4 or IPv6 (this would require the attacker to control that IP address, though). Similar attacks using other subjectAltName name types might be possible. Found and reported by kFYatek in #3498.
    • When checking X.509 CRLs, a certificate was only considered as revoked if its revocationDate was in the past according to the local clock if available. In particular, on builds without MBEDTLS_HAVE_TIME_DATE, certificates were never considered as revoked. On builds with MBEDTLS_HAVE_TIME_DATE, an attacker able to control the local clock (for example, an untrusted OS attacking a secure enclave) could prevent revocation of certificates via CRLs. Fixed by no longer checking the revocationDate field, in accordance with RFC 5280. Reported by yuemonangong in #3340. Reported independently and fixed by Raoul Strackx and Jethro Beekman in #3433.
    • 🛠 In (D)TLS record decryption, when using a CBC ciphersuites without the Encrypt-then-Mac extension, use constant code flow memory access patterns to extract and check the MAC. This is an improvement to the existing countermeasure against Lucky 13 attacks. The previous countermeasure was effective against network-based attackers, but less so against local attackers. The new countermeasure defends against local attackers, even if they have access to fine-grained measurements. In particular, this fixes a local Lucky 13 cache attack found and reported by Tuba Yavuz, Farhaan Fowze, Ken (Yihan) Bai, Grant Hernandez, and Kevin Butler (University of Florida) and Dave Tian (Purdue University).
    • 🛠 Fix side channel in RSA private key operations and static (finite-field) Diffie-Hellman. An adversary with precise enough timing and memory access information (typically an untrusted operating system attacking a secure enclave) could bypass an existing counter-measure (base blinding) and potentially fully recover the private key.
    • Fix a 1-byte buffer overread in mbedtls_x509_crl_parse_der(). Credit to OSS-Fuzz for detecting the problem and to Philippe Antoine for pinpointing the problematic code.
    • Zeroising of plaintext buffers in mbedtls_ssl_read() to erase unused application data from memory. Reported in #689 by Johan Uppman Bruce of Sectra.

    🛠 Bugfix

    • 🏗 Library files installed after a CMake build no longer have execute permission.
    • Use local labels in mbedtls_padlock_has_support() to fix an invalid symbol redefinition if the function is inlined. Reported in #3451 and fix contributed in #3452 by okhowang.
    • Fix the endianness of Curve25519 keys imported/exported through the PSA APIs. psa_import_key and psa_export_key will now correctly expect/output Montgomery keys in little-endian as defined by RFC7748. Contributed by Steven Cooreman in #3425.
    • 🛠 Fix build errors when the only enabled elliptic curves are Montgomery curves. Raised by signpainter in #941 and by Taiki-San in #1412. This also fixes missing declarations reported by Steven Cooreman in #1147.
    • 🛠 Fix self-test failure when the only enabled short Weierstrass elliptic curve is secp192k1. Fixes #2017.
    • PSA key import will now correctly import a Curve25519/Curve448 public key instead of erroring out. Contributed by Steven Cooreman in #3492.
    • 👉 Use arc4random_buf on NetBSD instead of rand implementation with cyclical lower bits. Fix contributed in #3540.
    • Fix a memory leak in mbedtls_md_setup() when using HMAC under low memory conditions. Reported and fix suggested by Guido Vranken in #3486.
    • 🛠 Fix bug in redirection of unit test outputs on platforms where stdout is defined as a macro. First reported in #2311 and fix contributed in #3528.

    🔄 Changes

    • 👍 Only pass -Wformat-signedness to versions of GCC that support it. Reported in #3478 and fix contributed in #3479 by okhowang.
    • Reduce the stack consumption of mbedtls_x509write_csr_der() which previously could lead to stack overflow on constrained devices. Contributed by Doru Gucea and Simon Leet in #3464.
    • Undefine the ASSERT macro before defining it locally, in case it is defined in a platform header. Contributed by Abdelatif Guettouche in #3557.
    • ⚡️ Update copyright notices to use Linux Foundation guidance. As a result, the copyright of contributors other than Arm is now acknowledged, and the years of publishing are no longer tracked in the source files. This also eliminates the need for the lines declaring the files to be part of MbedTLS. Fixes #3457.
    • Add the command line parameter key_pwd to the ssl_client2 and ssl_server2 example applications which allows to provide a password for the key file specified through the existing key_file argument. This allows the use of these applications with password-protected key files. Analogously but for ssl_server2 only, add the command line parameter key_pwd2 which allows to set a password for the key file provided through the existing key_file2 argument.

    ⚡️ 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.


    The SHA256 hashes for the archives are:

    d436ae4892bd80329ca18a3960052fbb42d3f1f46c7519711d6763621ca6cfa0 mbedtls-2.24.0.tar.gz
    d7b129288a957b1936ade3921504d5524e34a0dbe9f4d965df3416db9cfe0dae mbedtls-2.24.0.zip