CVE-2015-6564 Use after free in n/a

High 7.0 Published 24 Aug 2015 Updated 27 May 2026

Local attackers can gain privileges via a use-after-free in OpenSSH's monitor process by sending a malformed request.

Exploited in the wild: Not known
Login needed: Any signed-in user
Attackable: Local or same network only
Victim action needed: Not needed
Fix: Available

What is CVE-2015-6564?

CVE-2015-6564 is a high-severity use after free vulnerability in OpenSSH, published on 24 Aug 2015. It can only be exploited from the same machine or local network, with no action from the victim.

Official description

Use-after-free vulnerability in the mm_answer_pam_free_ctx function in monitor.c in sshd in OpenSSH before 7.0 on non-OpenBSD platforms might allow local users to gain privileges by leveraging control of the sshd uid to send an unexpectedly early MONITOR_REQ_PAM_FREE_CTX request.

Weakness: CWE-264, CWE-416

Which versions are affected by CVE-2015-6564?

It affects 1 product.

Products include OpenSSH.

How do I fix CVE-2015-6564?

Upgrade to a fixed version.

Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.

Is CVE-2015-6564 being exploited?

There is no known exploitation of CVE-2015-6564 in the wild and no public exploit code.

All OpenSSH vulnerabilities

Sources

Also known as DEBIAN-CVE-2015-6564, GHSA-cm6p-9f8w-c878, UBUNTU-CVE-2015-6564.