EUVD-2026-38412
GHSA-28f3-55mq-pp68
Severity by source
AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
Network-delivered via malicious server (AV:N), no privileges needed on attacker side (PR:N), but victim must initiate the connection (UI:R); impact is client-process termination only (A:L), no C or I impact.
Primary rating from Vendor (redhat).
CVSS VectorNVD
Lifecycle Timeline
3DescriptionNVD
A flaw was found in OpenSSH. A malicious SSH server can exploit a double free vulnerability in the Diffie-Hellman Group Exchange (DH-GEX) client path. This occurs during FIPS (Federal Information Processing Standards) mode known-group validation when the client processes attacker-controlled DH-GEX group parameters. Successful exploitation leads to client-side process termination, resulting in a Denial of Service (DoS).
AnalysisAI
Client-side Denial of Service in OpenSSH's Diffie-Hellman Group Exchange implementation allows a malicious SSH server to crash connecting clients running in FIPS mode. When a victim initiates an SSH connection to an attacker-controlled server, the server sends crafted DH-GEX group parameters that trigger a double free (CWE-415) during FIPS known-group validation, terminating the client process. No public exploit code has been identified at time of analysis, and the vulnerability is not listed in CISA KEV; however, the constraint that only FIPS-mode clients are affected limits real-world impact to regulated or government environments.
Technical ContextAI
OpenSSH implements the Diffie-Hellman Group Exchange (DH-GEX) key exchange mechanism, which allows the client and server to negotiate a modular group for the key exchange rather than using a fixed one. In FIPS (Federal Information Processing Standards) mode - a hardened operating mode required by U.S. government and regulated-industry deployments - OpenSSH performs additional validation of the server-supplied DH group parameters against a known-good list. CWE-415 (Double Free) indicates that during this FIPS known-group validation path, a memory region is freed twice, corrupting the heap. The root cause is a missing NULL-pointer reset or guard after the first free in the client-side DH-GEX processing code. Affected CPEs encompass Red Hat Enterprise Linux 6 through 10, Red Hat Hardened Images, and Red Hat OpenShift Container Platform 4, all of which ship and may enable OpenSSH's FIPS mode.
RemediationAI
No specific patched version of OpenSSH or Red Hat package has been identified in the available data; administrators should monitor https://access.redhat.com/security/cve/CVE-2026-55653 for errata as Red Hat releases fixes. Until a patch is available, the most effective compensating control for environments that do not strictly require FIPS mode is to disable FIPS mode operation on the SSH client, which eliminates the vulnerable code path entirely - note this may violate compliance mandates. For environments where FIPS mode is mandatory, restrict users from initiating SSH connections to untrusted or external servers by enforcing strict SSH known-hosts policies and connection-proxying through bastion hosts, reducing the attacker's ability to serve a malicious server to FIPS-mode clients. Blocking outbound SSH (port 22) to unauthorized destinations at the network perimeter is an additional layer. None of these compensating controls patch the underlying double free; apply the vendor errata as soon as it becomes available.
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Same weakness CWE-415 – Double Free
View allSame technique Denial Of Service
View allVendor StatusVendor
Debian
| Release | Status | Fixed Version | Urgency |
|---|---|---|---|
| bullseye | undetermined | 1:8.4p1-5+deb11u3 | - |
| bullseye (security) | undetermined | 1:8.4p1-5+deb11u7 | - |
| bookworm | undetermined | 1:9.2p1-2+deb12u10 | - |
| bookworm (security) | undetermined | 1:9.2p1-2+deb12u9 | - |
| trixie | undetermined | 1:10.0p1-7+deb13u4 | - |
| trixie (security) | undetermined | 1:10.0p1-7+deb13u2 | - |
| forky, sid | undetermined | 1:10.3p1-4 | - |
| (unstable) | fixed | undetermined | - |
SUSE
Severity: Moderate| Product | Status |
|---|---|
| SUSE Liberty Linux 10 | Fixed |
| SUSE Liberty Linux 8 | Fixed |
| SUSE Liberty Linux 9 | Fixed |
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External POC / Exploit Code
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