OpenSSL Security Advisory

[Matt Caswell]

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OpenSSL Security Advisory [28th May 2024]
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Use After Free with SSL_free_buffers (CVE-2024-4741)
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Severity: Low

Issue summary: Calling the OpenSSL API function SSL_free_buffers may cause
memory to be accessed that was previously freed in some situations

Impact summary: A use after free can have a range of potential consequences such
as the corruption of valid data, crashes or execution of arbitrary code.
However, only applications that directly call the SSL_free_buffers function are
affected by this issue. Applications that do not call this function are not
vulnerable. Our investigations indicate that this function is rarely used by
applications.

The SSL_free_buffers function is used to free the internal OpenSSL buffer used
when processing an incoming record from the network. The call is only expected
to succeed if the buffer is not currently in use. However, two scenarios have
been identified where the buffer is freed even when still in use.

The first scenario occurs where a record header has been received from the
network and processed by OpenSSL, but the full record body has not yet arrived.
In this case calling SSL_free_buffers will succeed even though a record has only
been partially processed and the buffer is still in use.

The second scenario occurs where a full record containing application data has
been received and processed by OpenSSL but the application has only read part of
this data. Again a call to SSL_free_buffers will succeed even though the buffer
is still in use.

While these scenarios could occur accidentally during normal operation a
malicious attacker could attempt to engineer a stituation where this occurs.
We are not aware of this issue being actively exploited.

The FIPS modules in 3.3, 3.2, 3.1 and 3.0 are not affected by this issue.

OpenSSL 1.0.2 is also not affected by this issue.

OpenSSL 3.3, 3.2, 3.1, 3.0 and 1.1.1 are vulnerable to this issue.

OpenSSL 3.3 users should upgrade to OpenSSL 3.3.1 once it is released.

OpenSSL 3.2 users should upgrade to OpenSSL 3.2.2 once it is released.

OpenSSL 3.1 users should upgrade to OpenSSL 3.1.6 once it is released.

OpenSSL 3.0 users should upgrade to OpenSSL 3.0.14 once it is released.

OpenSSL 1.1.1 users should upgrade to OpenSSL 1.1.1y once it is released
(premium support customers only).

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 e5093133c3 (for 3.3),
commit c88c3de510 (for 3.2), commit 704f725b96 (for 3.1) and commit b3f0eb0a29
(for 3.0) in the OpenSSL git repository. It is available to premium support
customers in commit f7a045f314 (for 1.1.1).

This issue was reported on 10th April 2024 by William Ahern (Akamai). The fix
was developed by Matt Caswell and Watson Ladd (Akamai).

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

URL for this Security Advisory:
https://www.openssl.org/news/secadv/20240528.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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