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Openssh CVE-2026-35387

| EUVDEUVD-2026-18402 MEDIUM
Always-Incorrect Control Flow Implementation (CWE-670)
2026-04-02 cve@mitre.org
Information Disclosure SSH Red Hat Suse Openssh Openbsd
6.5
CVSS 3.1 · NVD
Temporal: 3.1
View

Vulnerability Assessment

Weakness
CWE
CWE-670
ASVS 5.0
V15 - Secure Coding and Architecture Always-incorrect control flow
Impact

The risk profile indicates this is a low-priority vulnerability despite network accessibility. The CVSS score of 3.1 reflects restricted attack conditions: authentication is required (PR:L), attack complexity is high (AC:H), and impact is limited to integrity only with no confidentiality or availability effects. The integrity impact likely reflects potential for unauthorized key-based authentication using unexpected algorithm variants, rather than data corruption. The requirement for prior authentication and high complexity significantly constrains real-world exploitability. No EPSS probability, KEV status, or public proof-of-concept have been identified, suggesting minimal practical threat in typical deployments. Organizations implementing strict algorithm pinning policies face lower risk than those using permissive ECDSA whitelisting.
Exploit ScenarioDerived

An authenticated SSH user with a valid key for one ECDSA algorithm variant (e.g., ecdsa-sha2-nistp256) can authenticate using an unintended variant (e.g., ecdsa-sha2-nistp384) if the administrator mistakenly believed they had restricted authentication to the first variant. This requires the attacker to already possess a valid SSH credential and the target administrator to have misconfigured algorithm restrictions. The high attack complexity reflects the need for specific misconfigurations and prior authentication credentials, limiting practical exploitation to scenarios involving compromised or malicious internal users testing policy enforcement.
This Month Plan within 30 days. Why: MEDIUM severity (CVSS 4.0-6.9).
Patch available 0.0% exploitation probability (EPSS)

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AnalysisAIv1 – Apr 02, 2026

OpenSSH before 10.3 incorrectly interprets ECDSA algorithm specifications in PubkeyAcceptedAlgorithms and HostbasedAcceptedAlgorithms configuration options, allowing authenticated users to authenticate using unintended ECDSA variants. The vulnerability requires authenticated network access and high attack complexity, resulting in a low CVSS score of 3.1 with integrity impact but no confidentiality or availability loss. No public exploit code or active exploitation has been documented.

RemediationAI

Upgrade OpenSSH to version 10.3p1 or later, which corrects the ECDSA algorithm interpretation logic (https://www.openssh.org/releasenotes.html#10.3p1). For systems unable to upgrade immediately, implement strict algorithm specification in PubkeyAcceptedAlgorithms and HostbasedAcceptedAlgorithms by explicitly listing only desired ECDSA variants and avoiding catch-all patterns; additionally, review SSH key policies to minimize reliance on ECDSA authentication and consider preferring Ed25519-based keys where feasible. Consult the OpenSSH security advisory for distribution-specific patches (https://marc.info/?l=openssh-unix-dev&m=177513443901484&w=2).

Affected VersionsENISA

OpenSSH 0 <10.3

Affected Packages

euvd openssh fix: 10.3

Source: OSV (Open Source Vulnerabilities)

Affects your stack

Affects 1 package in euvd

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Technical ContextAI · show details

The vulnerability exists in OpenSSH's cryptographic algorithm negotiation logic, specifically in the parsing and interpretation of ECDSA algorithm lists in SSH configuration files. When an administrator specifies a single ECDSA algorithm in PubkeyAcceptedAlgorithms or HostbasedAcceptedAlgorithms (such as ecdsa-sha2-nistp256), the implementation incorrectly enables all ECDSA algorithm variants (ecdsa-sha2-nistp256, ecdsa-sha2-nistp384, ecdsa-sha2-nistp521) rather than restricting authentication to only the specified algorithm. This represents a failure in algorithm whitelisting logic (CWE-670: Improper Initialization with Hard-Coded Network Resource Configuration Data), where the intended fine-grained access control policy is undermined by overly permissive algorithm matching.

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Severity by source

NVD PRIMARY 6.5 MEDIUM
AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N
CIRCL (temporal) 3.1 LOW
SUSE 3.1 LOW
AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:N
Red Hat 3.1 LOW

Primary rating from NVD.

CVSS VectorNVD

Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
Low
Availability
None

Lifecycle Timeline

4
Severity Changed
Jul 24, 2026 - 21:22 NVD
LOW MEDIUM
CVSS changed
Jul 24, 2026 - 21:22 NVD
3.1 (LOW) 6.5 (MEDIUM)
Patch available
Apr 16, 2026 - 05:29 EUVD
10.3
CVE Published
Apr 02, 2026 - 17:16 nvd
LOW 3.1

DescriptionNVD

OpenSSH before 10.3 can use unintended ECDSA algorithms. Listing of any ECDSA algorithm in PubkeyAcceptedAlgorithms or HostbasedAcceptedAlgorithms is misinterpreted to mean all ECDSA algorithms.

Threat Intelligence Overview

EPSS Score
0.0%
Top 92% exploitable
Data Quality
6 sources
Confidence: High
EUVD NVD CVE.org EPSS Vulnrichment Vendor VulDB

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue
Severity MEDIUM
CISA KEV No
Public POC No
EPSS 0.0%
Patch available Yes
Active threat No
Deciding rule
MEDIUM severity (CVSS 4.0-6.9)
What every action level means
Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.
Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.
This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.
This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.
Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived
Scheduled
Exploitation
None
System Exposure· derived
Open
Automatable
No
Human Impact· derived
Medium
Technical Impact
Partial

Priority Score

32
Low Medium High Critical
KEV: 0
EPSS: 0
CVSS: +32
PoC: 0
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Attack Technique

Information Disclosure MEDIUM

Information disclosure occurs when an application unintentionally exposes sensitive data that aids attackers in reconnaissance or directly compromises security.

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Vendor StatusVendor

SUSE

Severity: Low
Product Status
SUSE Liberty Linux 10 Fixed
SUSE Liberty Linux 8 Fixed
SUSE Liberty Linux 9 Fixed
SLES15-SP5-CHOST-BYOS-SAP-CCloud Affected
SLES15-SP6-CHOST-BYOS Affected

References

Advisories & patches
ADVISORY https://access.redhat.com/errata/RHSA-2026:12389 ADVISORY https://access.redhat.com/errata/RHSA-2026:13380 ADVISORY https://access.redhat.com/errata/RHSA-2026:13381 ADVISORY https://access.redhat.com/errata/RHSA-2026:13383 ADVISORY https://access.redhat.com/errata/RHSA-2026:14937 ADVISORY https://access.redhat.com/errata/RHSA-2026:16059 ADVISORY https://access.redhat.com/errata/RHSA-2026:19069 ADVISORY https://access.redhat.com/errata/RHSA-2026:19219 ADVISORY https://access.redhat.com/errata/RHSA-2026:21275 ADVISORY https://access.redhat.com/errata/RHSA-2026:21298 ADVISORY https://access.redhat.com/errata/RHSA-2026:21398 ADVISORY https://access.redhat.com/errata/RHSA-2026:22329 ADVISORY https://access.redhat.com/errata/RHSA-2026:22564 ADVISORY https://access.redhat.com/errata/RHSA-2026:22648 ADVISORY https://access.redhat.com/errata/RHSA-2026:25096 ADVISORY https://nvd.nist.gov/vuln/detail/CVE-2026-35387 ADVISORY https://ubuntu.com/security/notices/USN-8222-1 ADVISORY https://vuldb.com/vuln/354955 REF https://marc.info/?l=openssh-unix-dev&m=177513443901484&w=2 REF https://www.openssh.org/releasenotes.html#10.3p1 REF https://www.openwall.com/lists/oss-security/2026/04/02/3

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