OpenSSL Security Advisory

[Tomas Mraz]

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OpenSSL Security Advisory [15th January 2024]
=============================================

Excessive time spent checking invalid RSA public keys (CVE-2023-6237)
=====================================================================

Severity: Low

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.

OpenSSL versions 3.0.0 to 3.0.12, 3.1.0 to 3.1.4 and 3.2.0 are vulnerable to
this issue.

OpenSSL versions 1.1.1 and 1.0.2 are not affected by this issue.

Due to the low severity of this issue we are not issuing new releases of
OpenSSL at this time. The fix will be included in the next releases when they
become available. The fix is also available in commit 0b0f7abf (for 3.2),
commit a830f551 (for 3.1) and commit 18c02492 (for 3.0) in the OpenSSL git
repository.

This issue was reported on 2nd November 2023 by OSS-Fuzz. The fix was
developed by Tomas Mraz.

General Advisory Notes
======================

URL for this Security Advisory:
https://www.openssl.org/news/secadv/20240115.txt

Note: the online version of the advisory may be updated with additional details
over time.

For details of OpenSSL severity classifications please see:
https://www.openssl.org/policies/secpolicy.html
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