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EximApplication

CVE-2025-67896

CRITICAL · 9.8 CVSS v3.1 Published 2025-12-14
Fix available
A fix is available. Upgrade to 4.99.1 or later.
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
Exim before 4.99.1, with certain non-default rate-limit configurations, allows a remote heap-based buffer overflow because database records are cast directly to internal structures without validation.

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

Exim mail server before version 4.99.1 contains a heap-based buffer overflow vulnerability in the rate-limit functionality. When non-default rate-limit configurations are enabled, database records are cast directly to internal structures without proper validation, allowing remote attackers to overflow the heap and potentially achieve remote code execution.

MitigationUpgrade Exim to version 4.99.1 or later. Until the upgrade can be applied, review and disable non-default rate-limit configurations as a temporary mitigation if feasible.

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
EximApplication
Affected:< 4.99.1

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 Exim version
    Run 'exim --version' or 'exim -v' to display the version number. Compare this to the affected range (versions prior to 4.99.1).
    Affected if The installed version is below 4.99.1
  2. Locate Exim configuration file
    Common paths are /etc/exim/exim.conf, /etc/exim4/exim4.conf, or /etc/exim/exim.cf. Check your system's default configuration location.
    Affected if Configuration file cannot be located for further rate-limit checks
  3. Check if rate-limit functionality is enabled
    Search the Exim configuration file for 'ratelimit' directives. Use 'grep -i ratelimit /etc/exim/exim.conf' or similar path.
    Affected if Ratelimit directives are present and configured (non-default settings)
  4. Inspect specific rate-limit configuration values
    Examine the ratelimit configuration lines in detail. Look for non-default values that enable the vulnerable code path, such as custom database backends or non-standard rate limits.
    Affected if Non-default rate-limit settings are configured (this enables the vulnerable code path)

A user is affected if they are running Exim version below 4.99.1 AND have non-default rate-limit configurations enabled in their Exim configuration.

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 4.99.1 or later
Fixed in 4.99.1
Interim mitigation

Upgrade Exim to version 4.99.1 or later. Until the upgrade can be applied, review and disable non-default rate-limit configurations as a temporary mitigation if feasible.

Recommended fix High confidence

Exim 4.99.1 or later

  1. 1. Check the currently installed Exim version: `exim --version` or `exim -bV`
  2. 2. Back up the current Exim configuration directory (typically /etc/exim/ or /etc/exim4/): `cp -r /etc/exim /etc/exim.backup`
  3. 3. Update your package repository to ensure you have access to the latest Exim packages
  4. 4. Upgrade Exim to version 4.99.1 or later: `apt-get update && apt-get install exim4` (Debian/Ubuntu) or `yum update exim` (RHEL/CentOS)
  5. 5. Verify the new version installed correctly: `exim --version`
  6. 6. Review the Exim configuration for rate-limit settings in the main configuration file
  7. 7. Test the configuration for syntax errors: `exim -bC /etc/exim/exim.conf -bT`
  8. 8. Restart the Exim service to apply the upgrade: `systemctl restart exim` or `systemctl restart exim4`
Caveat Review Exim release notes for 4.99.1 for any configuration syntax changes or deprecated options; rate-limit configuration may need adjustment

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

Fix this in Exim Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA4.0 h
22.0 hours of engineering $3,860
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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-2025-67896 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