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LibsshApplication

CVE-2023-3603

MEDIUM · 6.5 CVSS v3.1 Published 2023-07-21
Fix available
A fix is available. Upgrade to 0.8.9 or later.
See remediation →
71/100
Remediation priority · Elevated
Remotely reachable Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
A missing allocation check in sftp server processing read requests may cause a NULL dereference on low-memory conditions. The malicious client can request up to 4GB SFTP reads, causing allocation of up to 4GB buffers, which was not being checked for failure. This will likely crash the authenticated user's sftp server connection (if implemented as forking as recommended). For thread-based servers, this might also cause DoS for legitimate users. Given this code is not in any released versions, no security releases have been issued.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · moderate confidence

A missing allocation check in SFTP server processing of read requests allows a malicious authenticated client to request up to 4GB reads, causing allocation of large buffers without verifying allocation success. When memory allocation fails on low-memory systems, the NULL pointer dereference crashes the SFTP server connection in forking implementations or causes denial-of-service in thread-based servers.

MitigationSince this code is not in any released versions, no immediate patch is required; however, verify any custom or forked SFTP implementations do not contain this vulnerability before production use, and ensure proper allocation error handling is implemented.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
LibsshApplication
Affected:< 0.8.9

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify installed libssh version
    Run 'dpkg -l libssh-4' or 'rpm -q libssh' on Linux, or check Program Files\libssh directory on Windows. Alternatively, run 'ssh -V' or check library metadata with 'strings libssh.so | grep -i version'
    Affected if Version is lower than 0.8.9 (e.g., 0.8.x, 0.7.x series)
  2. Confirm SFTP server mode is in use
    Review sshd configuration files (typically /etc/ssh/sshd_config) for 'Subsystem sftp' lines, or check application logs for SFTP server initialization messages. Look for any custom SFTP server implementations using libssh
    Affected if SFTP subsystem is enabled or a custom libssh-based SFTP server is running
  3. Verify authentication methods allow remote client connections
    Check sshd_config for 'PasswordAuthentication yes', 'PubkeyAuthentication yes', or other authentication settings that permit remote users. For custom implementations, review authentication enforcement code
    Affected if Authenticated remote clients can connect to the SFTP service

Affected if libssh version is below 0.8.9 AND SFTP server functionality is enabled and accessible to authenticated clients, particularly on low-memory systems where allocation failures can occur.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 0.8.9 or later
Fixed in 0.8.9
Interim mitigation

Since this code is not in any released versions, no immediate patch is required; however, verify any custom or forked SFTP implementations do not contain this vulnerability before production use, and ensure proper allocation error handling is implemented.

Recommended fix High confidence
  1. No action is required. The vulnerable code was never released in any Libssh version.
  2. The issue existed in development code but was not included in any released version of Libssh.
  3. As stated in the official description, 'Given this code is not in any released versions, no security releases have been issued.'
  4. Continue using your current Libssh version as normal.

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Libssh Scoped from the published advisory
  • Consultation2.0 h
  • Implementation1.0 h
  • Testing2.0 h
  • Review / QA1.0 h
6.0 hours of engineering $1,060
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,696.

Scan for this in your stack

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2023-3603 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data