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Code InjectionWeakness · CWE-94

CVE-2024-39844

CRITICAL · 9.8 CVSS v3.1 Published 2024-07-03
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges 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
In ZNC before 1.9.1, remote code execution can occur in modtcl via a KICK.

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 · high confidence

ZNC versions before 1.9.1 contain a remote code execution vulnerability in the modtcl module where specially crafted KICK commands can be processed unsafely, allowing an attacker to execute arbitrary code on the server.

MitigationUpgrade ZNC to version 1.9.1 or later. If the modtcl module is not required, consider disabling it as a defense-in-depth measure until the upgrade can be applied.

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

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
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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. Determine installed ZNC version
    Run `znc --version` or check the ZNC service version through your package manager (e.g., `dpkg -l znc`, `rpm -qi znc`, or `znc --version`). Compare the version number to 1.9.1.
    Affected if The installed version is before 1.9.1 (e.g., 1.9.0, 1.8.x, or earlier).
  2. Identify if modtcl module is loaded
    Check your ZNC configuration file (typically ~/.znc/configs/znc.conf or /etc/znc/znc.conf) for the modtcl module listed under LoadModule settings, or run `znc --makepass` and examine loaded modules via the control panel if accessible.
    Affected if The modtcl module is present in the LoadModule list or is actively loaded in your ZNC instance.
  3. Verify modtcl module is reachable via IRC
    If modtcl is loaded, confirm it can process KICK commands from any IRC channel where ZNC is present. This is a functional check: if the module handles KICK events, it processes them unsafely when crafted maliciously.
    Affected if The modtcl module is loaded and capable of processing KICK commands from remote users on any channel where ZNC operates.

You are affected if your ZNC version is earlier than 1.9.1 AND the modtcl module is loaded and operational in your environment.

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
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade ZNC to version 1.9.1 or later. If the modtcl module is not required, consider disabling it as a defense-in-depth measure until the upgrade can be applied.

Recommended fix High confidence

ZNC 1.9.1 or later

  1. 1. Check current ZNC version: znc --version
  2. 2. Backup ZNC configuration directory (typically ~/.znc or /etc/znc)
  3. 3. Download ZNC 1.9.1 or later from the official GitHub releases: https://github.com/znc/znc/releases
  4. 4. Stop the running ZNC service: systemctl stop znc or pkill znc
  5. 5. Install the new ZNC version using your system's package manager or compile from source
  6. 6. Verify the installation: znc --version (should show 1.9.1 or higher)
  7. 7. Start ZNC service: systemctl start znc or znc
Caveat Review ZNC 1.9.x release notes for any module or configuration changes from prior versions

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

Have this fixed Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing3.0 h
  • Review / QA2.0 h
9.0 hours of engineering $1,570
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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-2024-39844 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