CVE-2025-22869

What it actually does

SSH servers handling file transfer protocols allow clients to initiate connections and perform key exchange at an arbitrarily slow rate or not at all, causing the server to allocate memory for pending content that is never fully transmitted or processed.

Why it matters to the business

Attackers can exhaust server memory and CPU resources, leading to denial of service for legitimate file transfer operations and potential disruption of secure data movement workflows.

How an attack unfolds

An attacker opens multiple SSH connections to a vulnerable server implementing file transfer protocols and deliberately delays or stalls the key exchange phase, forcing the server to buffer incoming data without completing authentication or transmission.

How to fix it

Apply vendor patches for affected SSH implementations when released; enforce connection timeouts and rate limiting on key exchange phases; consider disabling file transfer subsystems if not required.

How to confirm the fix worked

Review server logs and resource utilization metrics for stalled key exchange sessions; test connectivity with controlled slow-handshake clients to confirm timeout enforcement after updates.

Typical attack path

1. Establish TCP connection to the SSH server port
2. Begin SSH protocol negotiation and initiate key exchange
3. Transmit initial packets then pause or send data extremely slowly
4. Repeat across many concurrent connections to amplify resource consumption
5. Observe server memory growth and eventual service degradation or crash

How to detect it

Inspect SSH daemon logs for high volumes of connections stuck in key exchange state; correlate with system resource monitors showing sustained memory growth without corresponding completed sessions.

What your security team should do

• Monitor for availability of upstream fixes and schedule patching
• Implement network-level connection rate limiting and idle timeouts for SSH
• Audit SSH configurations to restrict unnecessary file transfer features
• Add alerting on anomalous memory usage tied to SSH processes