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Date: Wed, 19 Jul 2023 11:35:37 +0000
From: Tomas Mraz <>
Subject: OpenSSL Security Advisory

Hash: SHA256

OpenSSL Security Advisory [19th July 2023]

Excessive time spent checking DH keys and parameters (CVE-2023-3446)

Severity: Low

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. One of those
checks confirms that the modulus ("p" parameter) is not too large. Trying to use
a very large modulus is slow and OpenSSL will not normally use a modulus which
is over 10,000 bits in length.

However the DH_check() function checks numerous aspects of the key or parameters
that have been supplied. Some of those checks use the supplied modulus value
even if it has already been found to be too large.

An application that calls DH_check() and supplies a key or parameters obtained
from an untrusted source could be vulernable 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

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.

OpenSSL 3.1, 3.0, 1.1.1 and 1.0.2 are vulnerable to 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 fc9867c1 (for 3.1),
commit 1fa20cf2 (for 3.0) and commit 8780a896 (for 1.1.1) in the OpenSSL git
repository. It is available to premium support customer in commit 9a0a4d3c (for

OSSfuzz first detected and automatically reported this issue on 25th June
2023 using a fuzzer recently added to OpenSSL written by Kurt Roeckx. The fix
was developed by Matt Caswell.

General Advisory Notes

URL for this Security Advisory:

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

For details of OpenSSL severity classifications please see:

OpenSSL 1.1.1 will reach end-of-life on 2023-09-11. After that date security
fixes for 1.1.1 will only be available to premium support customers.


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