CVE-2025-8114: Libssh Buffer Overflow Vulnerability

CVE-2025-8114 Overview

CVE-2025-8114 is a NULL pointer dereference flaw [CWE-476] in libssh, an open-source library implementing the Secure Shell (SSH) protocol. The defect occurs during session ID calculation in the key exchange (KEX) process. When cryptographic allocation functions fail, the code dereferences a NULL pointer instead of handling the error. The result is a crash of either the SSH client or server process.

The issue affects applications and services that depend on libssh for SSH functionality. Exploitation requires local access and specific conditions that cause memory allocation to fail, limiting practical impact to availability.

Critical Impact
Successful triggering causes libssh-based clients or servers to crash, producing a denial of service against SSH-dependent workflows.

Affected Products

libssh (versions prior to the fix in commits 53ac23ded and 65f363c9)
Red Hat Enterprise Linux packages distributing vulnerable libssh builds (see RHSA-2026:18683)
Downstream applications linking vulnerable libssh releases

Discovery Timeline

2025-07-24 - CVE-2025-8114 published to the National Vulnerability Database
2026-09-01 - Last updated in NVD database

Technical Details for CVE-2025-8114

Vulnerability Analysis

The flaw resides in libssh's key exchange handling. During SSH session establishment, both peers compute a session identifier derived from cryptographic hash operations over exchange parameters. These operations allocate hash contexts and buffers through libssh's crypto backend wrappers.

When an allocation inside those cryptographic helpers fails, the helper returns a NULL pointer. The calling code in the session ID computation path does not validate the return value before dereferencing it. The process then faults and terminates. For a server, this ends the daemon or worker handling the connection. For a client, it terminates the client process mid-handshake.

The attacker must be local and able to influence memory conditions. The impact is limited to availability. Confidentiality and integrity are not affected.

Root Cause

The root cause is missing NULL return checks after cryptographic allocation calls in the KEX session ID logic. Error paths from allocation failures were not propagated. Instead, execution continued and dereferenced an invalid pointer, producing an unhandled exception [CWE-476].

Attack Vector

Triggering the condition requires local access and the ability to constrain resources so that cryptographic allocations fail at the right point in the KEX. An attacker meeting these conditions can repeatedly initiate SSH handshakes to crash the targeted libssh process. Automated services that restart aggressively may enter a crash loop and consume additional system resources.

No verified public exploit is available. The vulnerability has not been added to the CISA Known Exploited Vulnerabilities catalog.

Detection Methods for CVE-2025-8114

Indicators of Compromise

Repeated unexpected termination of SSH server daemons or client processes linked against libssh.
Core dumps or segmentation faults referencing libssh KEX functions such as session ID derivation routines.
Spikes in failed SSH handshake attempts from local accounts followed by process crashes.

Detection Strategies

Monitor system logs (journalctl, /var/log/messages, dmesg) for SIGSEGV events in binaries that link libssh.so.
Enable crash reporting (systemd-coredump, ABRT) and inspect stack traces for frames inside libssh KEX code paths.
Inventory installed libssh package versions across the fleet and flag hosts still running pre-patch builds.

Monitoring Recommendations

Alert on local user activity that initiates abnormally high rates of SSH connections to localhost or loopback services.
Track service restart counts for SSH-dependent daemons and treat crash loops as investigation triggers.
Correlate memory pressure events with SSH process termination to identify allocation-failure conditions.

How to Mitigate CVE-2025-8114

Immediate Actions Required

Apply vendor-supplied updates that include libssh commits 53ac23ded4cb2c5463f6c4cd1525331bd578812d and 65f363c9.
On Red Hat systems, install the packages listed in Red Hat Security Advisory RHSA-2026:18683.
Restart all services and long-running processes that dynamically link libssh.so after patching.

Patch Information

The upstream fix is published in the libssh Security Advisory CVE-2025-8114 and delivered through libssh Commit 53ac23ded and libssh Commit 65f363c9. Distribution-specific details are tracked in Red Hat CVE-2025-8114 Details and Red Hat Bugzilla Entry #2383220.

Workarounds

Restrict local shell access to trusted users to reduce the population able to influence allocation conditions.
Apply memory and process resource limits (ulimit, cgroups) to prevent attacker-controlled resource starvation of SSH services.
Configure service managers to rate-limit automatic restarts of SSH daemons to contain crash-loop effects until patches are applied.

bash

# Verify installed libssh version on RHEL-based systems
rpm -q libssh

# Apply vendor updates
sudo dnf update libssh

# Restart SSH daemon after patching
sudo systemctl restart sshd