Pre-authentication Denial of Service attack in OpenSSH - CVE-2025-26466
CVSSv3 Score: 5.9 CVE-2025-26466A flaw was found in the OpenSSH package. For each ping packet the SSH server receives, a pong packet is allocated in a memory buffer and stored in a queue of packages. It is only freed when the server/client key exchange has finished. A malicious client may keep sending such packages, leading to an uncontrolled increase in memory consumption on the server side. Consequently, the server may become unavailable, resulting in a denial of service attack. Revised on 2026-05-25 00:00:00
CSIRTS triage
- What
- A flaw allows a malicious client to cause a denial of service by consuming server memory.
- Who is affected
- OpenSSH servers that receive ping packets from malicious clients.
- Urgency
- Remediation is necessary as it can lead to server unavailability.
- Action
- Implement measures to limit or monitor incoming ping packets.
AI-assisted analysis generated from the source advisory — verify against the original.
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Details
Original advisory: https://fortiguard.fortinet.com/psirt/FG-IR-25-122
Exploitation outlook
EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.
- Elevated exploitation riskCVE-2025-2646638.5% 30-day exploitation probability — well above the norm. Schedule remediation this cycle. Riskier than 98% of all scored CVEs.
Referenced CVEs
| CVE | CSIRTS overview | External |
|---|---|---|
| CVE-2025-26466 | coverage & exploitation status | NVD · CVE.org |
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