Excessive time spent checking invalid RSA public keys

Vulnerability Description

Issue summary: Checking excessively long invalid RSA public keys may take a long time. Impact summary: Applications that use the function EVP_PKEY_public_check() to check RSA public keys may experience long delays. Where the key that is being checked has been obtained from an untrusted source this may lead to a Denial of Service. When function EVP_PKEY_public_check() is called on RSA public keys, a computation is done to confirm that the RSA modulus, n, is composite. For valid RSA keys, n is a product of two or more large primes and this computation completes quickly. However, if n is an overly large prime, then this computation would take a long time. An application that calls EVP_PKEY_public_check() and supplies an RSA key obtained from an untrusted source could be vulnerable to a Denial of Service attack. The function EVP_PKEY_public_check() is not called from other OpenSSL functions however it is called from the OpenSSL pkey command line application. For that reason that application is also vulnerable if used with the '-pubin' and '-check' options on untrusted data. The OpenSSL SSL/TLS implementation is not affected by this issue. The OpenSSL 3.0 and 3.1 FIPS providers are affected by this issue.

References

• https://www.openssl.org/news/secadv/20240115.txt
• https://github.com/openssl/openssl/commit/18c02492138d1eb8b6548cb26e7b625fb2414a2a
• https://github.com/openssl/openssl/commit/a830f551557d3d66a84bbb18a5b889c640c36294
• https://github.com/openssl/openssl/commit/0b0f7abfb37350794a4b8960fafc292cd5d1b84d