CVE-2023-3817

A vulnerability was found in OpenSSL. This security issue occurs because the applications that use the DH_check(), DH_check_ex(), or EVP_PKEY_param_check() functions to check a DH key or DH parameters may experience long delays. Where the key or parameters that are being checked have been obtained from an untrusted source may lead to a denial of service.

Issue summary: Checking excessively long DH keys or parameters may be very slow. Impact summary: Applications that use the functions DH_check(), DH_check_ex() or EVP_PKEY_param_check() to check a DH key or DH parameters may experience long delays. Where the key or parameters that are being checked have been obtained from an untrusted source this may lead to a Denial of Service. The function DH_check() performs various checks on DH parameters. After fixing CVE-2023-3446 it was discovered that a large q parameter value can also trigger an overly long computation during some of these checks. A correct q value, if present, cannot be larger than the modulus p parameter, thus it is unnecessary to perform these checks if q is larger than p. An application that calls DH_check() and supplies a key or parameters obtained from an untrusted source could be vulnerable to a Denial of Service attack. The function DH_check() is itself called by a number of other OpenSSL functions. An application calling any of those other functions may similarly be affected. The other functions affected by this are DH_check_ex() and EVP_PKEY_param_check(). Also vulnerable are the OpenSSL dhparam and pkeyparam command line applications when using the "-check" option. The OpenSSL SSL/TLS implementation is not affected by this issue. The OpenSSL 3.0 and 3.1 FIPS providers are not affected by this issue.

It was discovered that checking excessively long DH keys or parameters may be very slow. A remote attacker could possibly use this issue to cause OpenSSL to consume resources, resulting in a denial of service. After the fix for CVE-2023-3446 Bernd Edlinger discovered that a large q parameter value can also trigger an overly long computation during some of these checks. A remote attacker could possibly use this issue to cause OpenSSL to consume resources, resulting in a denial of service.