Raw vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:HSummary
CVE-2025-26466 is a medium-severity Allocation of Resources Without Limits or Throttling (CWE-770) vulnerability in Openbsd Openssh. Its CVSS base score is 5.9 (Medium).
Operationally, exploitation aligns with the MITRE ATT&CK technique Network Denial of Service (T1498); ranked in the top 2% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified map to AC-10 (Concurrent Session Control) and SC-6 (Resource Availability) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
CVE-2025-26466, published on 2025-02-28, is a vulnerability in the OpenSSH package affecting the SSH server component. The flaw stems from improper memory management during the handling of ping packets received before key exchange completion. For each ping packet, the server allocates a pong packet in a memory buffer and stores it in a queue, but these are only freed after the server/client key exchange finishes. This allows a malicious client to send repeated ping packets, resulting in uncontrolled memory consumption and potential server unavailability, classified under CWE-770 (Allocation of Resources Without Limits or Throttling). The CVSS v3.1 base score is 5.9 (AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H).
A remote, unauthenticated attacker can exploit this vulnerability over the network by continuously sending ping packets to the SSH server prior to key exchange. The high attack complexity (AC:H) likely arises from the need to precisely time and sustain the packet flood without triggering other defenses or completing the handshake. Successful exploitation leads to denial of service through memory exhaustion, rendering the server unresponsive, with no impact on confidentiality or integrity.
Mitigation details are provided in vendor advisories, including the Red Hat security bulletin at https://access.redhat.com/security/cve/CVE-2025-26466, the associated Bugzilla report at https://bugzilla.redhat.com/show_bug.cgi?id=2345043, and analyses from Qualys (https://www.qualys.com/2025/02/18/openssh-mitm-dos.txt) and security mailing lists such as oss-sec (https://seclists.org/oss-sec/2025/q1/144) and fulldisclosure (http://seclists.org/fulldisclosure/2025/Feb/18). Security practitioners should consult these for patch availability and workarounds specific to affected OpenSSH versions.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2025-5920
Vulnerability Data
A 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…
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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.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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- 5 hardening rules · 3 OS baselines
V15.4.4
Mitigating Controls (NIST 800-53 r5) AI
Directly enforces a hard limit on concurrent sessions, structurally preventing unbounded resource allocation.
Requires explicit allocation of resources by priority or quota, directly stopping unlimited allocation.
Imposes a limit on consecutive invalid attempts, preventing one specific class of unbounded resource consumption.
Reduces impact of resulting DoS events without preventing the underlying lack of allocation limits.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Monitoring capacity and taking action to maintain availability directly reduces unchecked resource allocation.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Baseline comparison of CPU, memory and bandwidth usage helps surface uncontrolled resource allocations before they cause service degradation.
Capacity projections and elasticity measures ensure that allocation requests are bounded and can be throttled, reducing the window in which an attacker can force unbounded resource reservations.
Defining retention periods and deletion schedules for backup copies prevents indefinite accumulation of data on storage media without corresponding resource-management controls.
Architectural redundancy and automatic failover limit the impact of an attacker who forces excessive allocations, because spare capacity can absorb the load until the primary instance recovers.
Documented incident response procedures that include activation of continuity plans and controlled recovery help ensure that resource consumption triggered by an incident is bounded and managed rather than left unbounded.
Mandating tested continuity procedures that preserve or replace resource-limiting controls prevents an attacker from exploiting the absence of throttling mechanisms during an outage.
Hardening callouts derived
Configuration rules from DISA STIG baselines that bear on weaknesses of the type cited by this CVE. Each rule is shown with the relationship its mapping actually records, against the CWE it was authored against. Derived via CVE→CWE over `controls_xwalks` (authoritative rows only; rows rated `none` are excluded).
Oracle Linux 8 (2 rules)
- V-248552 OL 8 must be configured so that all network connections associated with SSH traffic terminate after becoming unresponsive. prevents CWE-770
- V-248553 OL 8 must be configured so that all network connections associated with SSH traffic are terminated after 10 minutes of becoming unresponsive. prevents CWE-770
Oracle Linux 9 (2 rules)
- V-271710 OL 9 must be configured so that all network connections associated with SSH traffic are terminated after 10 minutes of becoming unresponsive. prevents CWE-770
- V-271709 OL 9 must be configured so that all network connections associated with SSH traffic terminate after becoming unresponsive. prevents CWE-770
RHEL 8 (1 rule)
- V-230244 RHEL 8 must be configured so that all network connections associated with SSH traffic terminate after becoming unresponsive. prevents CWE-770