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libssh EUVDEUVD-2026-46177

| CVE-2026-59843 MEDIUM
Uncontrolled Resource Consumption (CWE-400)
2026-07-21 redhat GHSA-4846-7xwg-pw5m
Denial Of Service Red Hat Enterprise Linux 10 Red Hat Enterprise Linux 8 Red Hat Enterprise Linux 9 Red Hat Hardened Images Red Hat
6.5
CVSS 3.1 · Vendor: redhat
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Severity by source

Vendor (redhat) PRIMARY
6.5 MEDIUM
AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
vuln.today AI
6.5 MEDIUM

Authenticated network attacker sends a crafted channel-open message; zero packet size causes unbounded CPU loop giving A:H with no confidentiality or integrity impact.

3.1 AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
4.0 AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
SUSE
MEDIUM
qualitative
Red Hat
6.5 MEDIUM
qualitative

Primary rating from Vendor (redhat).

CVSS VectorVendor: redhat

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

Lifecycle Timeline

2
Analysis Generated
Jul 21, 2026 - 12:02 vuln.today
CVE Published
Jul 21, 2026 - 11:16 cve.org
MEDIUM 6.5

DescriptionCVE.org

A flaw was found in libssh. A remote authenticated peer can advertise a zero maximum packet size in SSH_MSG_CHANNEL_OPEN, causing later channel writes to loop indefinitely and consume CPU, leading to denial of service.

AnalysisAI

CPU exhaustion via malformed SSH channel negotiation in libssh allows an authenticated remote peer to cause indefinite server-side looping and denial of service. By advertising a zero maximum packet size in SSH_MSG_CHANNEL_OPEN, the attacker forces subsequent channel writes into an infinite loop, fully consuming CPU on the affected host. This affects libssh as shipped in Red Hat Enterprise Linux 8, 9, and 10 and Red Hat Hardened Images; no public exploit or CISA KEV listing has been identified at time of analysis.

Technical ContextAI

libssh is a C library implementing the SSHv2 protocol, used in applications requiring embedded SSH client or server functionality. The SSH channel mechanism uses SSH_MSG_CHANNEL_OPEN to negotiate parameters including the remote maximum packet size, which governs how much data can be sent per channel write. When a peer advertises a maximum packet size of zero, any subsequent write operation that divides or iterates based on that value enters an unreachable-exit loop, consuming CPU without bound. The root cause is absent or insufficient input validation of the negotiated packet size prior to its use in write-loop logic - conceptually equivalent to CWE-835 (Loop with Unreachable Exit Condition) or CWE-400 (Uncontrolled Resource Consumption), though no formal CWE is assigned in this record. CPE data confirms the affected surface is the libssh package bundled within Red Hat Enterprise Linux 8 (cpe:2.3:a:red_hat:red_hat_enterprise_linux_8), RHEL 9, RHEL 10, and Red Hat Hardened Images.

RemediationAI

Apply the libssh package update provided by Red Hat for the affected RHEL major versions (8, 9, 10) and Hardened Images as detailed at https://access.redhat.com/security/cve/CVE-2026-59843. An exact patched package version is not independently confirmed in the available data - consult the Red Hat advisory and errata directly for the specific build to install. As a compensating control while awaiting the patch, restrict SSH access to the minimal set of trusted authenticated users via AllowUsers or AllowGroups directives in sshd_config; this reduces the attacker pool but does not eliminate risk from a compromised authorized account. Additionally, consider deploying connection-rate limiting and maximum session controls (MaxSessions, MaxStartups in sshd_config) to limit the CPU impact of an ongoing attack. Note that these mitigations do not prevent exploitation by a legitimately authenticated malicious user - patching is the only definitive fix.

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Same weakness CWE-400 – Uncontrolled Resource Consumption

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Same technique Denial Of Service

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Vendor StatusVendor

SUSE

Severity: Moderate
Product Status
SUSE Linux Enterprise Module for Basesystem 15 SP7 Affected
SUSE Linux Enterprise Server 15 SP7 Affected
SUSE Linux Enterprise Desktop 15 SP7 Affected
SUSE Linux Enterprise Server for SAP Applications 15 SP7 Affected
SUSE Linux Enterprise High Performance Computing 15 SP7 Affected

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EUVD-2026-46177 vulnerability details – vuln.today
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