Vulnerability CVE-2023-6237
Published: 2024-04-25

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
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