EUVD-2026-38412
GHSA-28f3-55mq-pp68
Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain
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AccessAttacker deploys malicious SSH server
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DeliveryVictim on FIPS-mode client initiates SSH connection
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ExploitServer presents crafted DH-GEX group parameters
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ExecutionFIPS known-group validation processes attacker-supplied parameters
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PersistDouble free corrupts client heap
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ImpactSSH client process terminates (DoS)
Vulnerability Assessment
| Weakness |
CWE
ASVS 5.0
V15 - Secure Coding and Architecture Double free prevention
|
| Exploitation Conditions | Exploitation requires two simultaneous conditions: (1) the OpenSSH client must be operating in FIPS mode - this is a non-default configuration typically enforced via system-wide FIPS policy (e.g., 'fips-mode-setup --enable' on RHEL) and is not present in standard installations; and (2) the victim user must actively initiate an SSH connection (UI:R) to a server controlled by the attacker. What limits exploitation: FIPS mode is only active in regulated or explicitly hardened deployments; the impact is restricted to client process termination with no lateral movement, credential theft, or code execution; and the attacker must be positioned to serve as or impersonate an SSH server the victim is connecting to. |
| Impact | The CVSS 3.1 base score of 4.3 (Medium) reflects an availability-only impact limited to the client process (A:L, S:U), with no confidentiality or integrity consequences. The attack vector is network (AV:N) with low complexity (AC:L) but requires user interaction (UI:R) - the victim must actively initiate an SSH connection to a server under attacker control. EPSS data is not provided, so exploitation probability cannot be quantitatively assessed. The vulnerability is not listed in CISA KEV, and no POC is known, indicating this is not currently being weaponized. The most significant real-world limiting factor is the FIPS mode requirement: exploitation is only possible against clients explicitly configured to run in FIPS mode, which is a non-default, regulated-environment configuration. For FIPS-mode RHEL and OpenShift environments - common in federal, defense, and financial sectors - this is a credible client-side availability risk, but the blast radius is process termination of the SSH client only, not the server or any broader system compromise. Overall, this is a targeted, low-severity issue for non-FIPS deployments; moderate operational concern only for FIPS-mandated environments. |
| Exploit ScenarioDerived | An attacker operating a malicious SSH server on the internet (or on an internal network via server compromise or ARP poisoning) waits for a victim on a FIPS-mode RHEL or OpenShift system to initiate an SSH connection. When the victim's OpenSSH client begins the DH-GEX key exchange, the malicious server returns specially crafted group parameters that trigger the double free during FIPS known-group validation, causing the client process to crash and aborting the session. No public exploit code has been identified; the attack requires the victim to connect to an attacker-controlled endpoint. |
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Alert meAnalysisAIv1 – Jun 23, 2026
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.
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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Technical ContextAI · show details
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.
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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
2DescriptionNVD
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).
Threat Intelligence Overview
NVD
CVE.org
EPSS
Vulnrichment
VulDB
How this decision was reached
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What every action level means
SSVC AssessmentENISA
Priority Score
Attack Technique
Denial of Service attacks render applications or systems unavailable by overwhelming resources or triggering failure conditions.
Affected Products (CPE)NVD
GNU Bash through 4.3 processes trailing strings after function definitions in the values of environment variables, which
GNU Bash through 4.3 bash43-026 does not properly parse function definitions in the values of environment variables, whi
GNU Bash through 4.3 bash43-025 processes trailing strings after certain malformed function definitions in the values of
freeSSHd.exe in freeSSHd through 1.2.6 allows remote attackers to bypass authentication via a crafted session, as demons
GNU Bash through 4.3 bash43-026 does not properly parse function definitions in the values of environment variables, whi
The PKCS#11 feature in ssh-agent in OpenSSH before 9.3p2 has an insufficiently trustworthy search path, leading to remot
OpenSSH server (sshd) 9.1 introduced a double-free vulnerability during options.kex_algorithms handling. Rated medium se
sshd in OpenSSH before 7.3, when SHA256 or SHA512 are used for user password hashing, uses BLOWFISH hashing on a static
The kbdint_next_device function in auth2-chall.c in sshd in OpenSSH through 6.9 does not properly restrict the processin
The auth_password function in auth-passwd.c in sshd in OpenSSH before 7.3 does not limit password lengths for password a
Remote code execution in OpenSSH's sshd server (regression of CVE-2006-5051) allows unauthenticated remote attackers to
An issue was discovered in OpenSSH 7.9. Rated medium severity (CVSS 5.9), this vulnerability is remotely exploitable, no
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 |
Exploit-DB