CVE-2026-73282: OpenSSH Use-After-Free Vulnerability

CVE-2026-73282 Overview

CVE-2026-73282 is a use-after-free vulnerability in the OpenSSH client (ssh) affecting versions before 10.5. The flaw resides in the handling of realloc data during concurrent remote-forwarding operations. When a specific pair of remote-forwarding requests execute concurrently, the client may reference memory that has already been freed, leading to undefined behavior. The issue is tracked as CWE-416: Use After Free and is addressed in OpenSSH 10.5.

Critical Impact
A remote peer can trigger a use-after-free condition in the OpenSSH client, potentially causing information disclosure, integrity loss, or crashes during remote port forwarding sessions.

Affected Products

OpenSSH ssh client versions prior to 10.5
Systems using remote port forwarding (-R) with OpenSSH clients
Distributions bundling vulnerable OpenSSH client packages

Discovery Timeline

2026-08-11 - CVE-2026-73282 published to NVD
2026-08-11 - Last updated in NVD database

Technical Details for CVE-2026-73282

Vulnerability Analysis

The vulnerability exists in the OpenSSH client's remote-forwarding code path. When a client requests remote forwarding using the -R option, the server establishes a listener and communicates channel state back to the client. The client tracks these forwardings in dynamically allocated structures managed with realloc.

When two remote-forwarding operations occur concurrently, one operation may free or reallocate a buffer while another still holds a reference to the original allocation. The stale pointer is then dereferenced, producing use-after-free behavior. Depending on allocator state and timing, the outcome ranges from a process crash to memory disclosure or corruption of adjacent heap metadata.

The attack requires network positioning and specific timing conditions, which raises exploitation complexity. However, no authentication or user interaction is required beyond the target initiating an SSH session with the malicious peer.

Root Cause

The root cause is improper lifetime management of realloc-backed data during concurrent state changes in remote-forwarding logic. realloc may return a new pointer and invalidate the previous allocation, but concurrent code paths retain and dereference the old pointer. This constitutes a classic CWE-416 condition triggered by a race between forwarding operations.

Attack Vector

An attacker who controls or is positioned to influence an SSH server can send crafted responses that cause the client to execute the vulnerable concurrent forwarding paths. The vulnerability is network-reachable, requires no privileges, and requires no user interaction beyond an established SSH session with remote forwarding. Successful exploitation impacts confidentiality and integrity at a limited scope; availability is not directly affected per the published CVSS metrics.

Refer to the OpenSSH Release Notes 10.5 for the vendor's technical description and patch details.

Detection Methods for CVE-2026-73282

Indicators of Compromise

Unexpected crashes or segmentation faults from ssh client processes using -R remote forwarding
Core dumps referencing OpenSSH channel or forwarding structures
SSH client sessions that terminate abnormally shortly after establishing multiple remote-forwarding channels

Detection Strategies

Inventory OpenSSH client versions across endpoints and servers, flagging any version below 10.5
Monitor for anomalous ssh process termination signals (SIGSEGV, SIGABRT) in system logs and journald output
Correlate outbound SSH sessions with untrusted hosts against process crash telemetry

Monitoring Recommendations

Enable audit logging for SSH client invocations that use the -R flag, especially against external hosts
Ingest system crash reports and OpenSSH client logs into a centralized logging platform for correlation
Track package versions of openssh-client through configuration management or endpoint inventory tooling

How to Mitigate CVE-2026-73282

Immediate Actions Required

Upgrade OpenSSH client packages to version 10.5 or later on all systems
Audit and restrict use of remote port forwarding (-R) to trusted SSH servers only
Apply distribution security updates as vendors backport the fix to supported OpenSSH branches

Patch Information

The issue is fixed in OpenSSH 10.5. Details are documented in the OpenSSH Release Notes 10.5. Linux distributions typically publish backported updates through their security advisory channels; apply vendor updates through apt, dnf, yum, or equivalent package managers as they become available.

Workarounds

Avoid establishing remote port forwardings against untrusted or unknown SSH servers
Disable remote forwarding at the client level using RemoteForward restrictions in ~/.ssh/config where the feature is not required
Use Match blocks in ssh_config to limit forwarding behavior to specific trusted hosts

bash

# Example ssh_config hardening to limit remote forwarding to trusted hosts
Host *
    ClearAllForwardings yes

Host trusted-bastion.example.com
    ClearAllForwardings no
    RemoteForward 8080 localhost:8080