CVE-2026-48840
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 · uneditedExim 4.88 before 4.99.4, in some proxy configurations, mishandles certain short payloads, leading to disclosure of uninitialized stack memory values to a client.
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 confidenceExim versions 4.88 through 4.99.3 contain an information disclosure vulnerability where certain short payloads are mishandled in specific proxy configurations, causing uninitialized stack memory to be leaked to connected clients.
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>= 4.88, < 4.99.4CVSS 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
- Low
- Integrity
- None
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
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 checksWork through these to decide whether this CVE applies to you.
-
Check installed Exim versionRun 'exim --version' or query via package manager (dpkg -l exim4, rpm -q exim, etc.)Affected if Version is >= 4.88 and < 4.99.4
-
Locate Exim configuration fileExamine /etc/exim/exim.conf, /etc/exim4/exim4.conf, or the active configuration file as shown by 'exim -bP'Affected if Configuration file exists and Exim is running
-
Identify proxy configuration usageSearch configuration for proxy-related directives or settings (such as 'proxy', 'forwarder', or relay proxy features)Affected if Proxy configuration that routes connections through the vulnerable code path is enabled and active
-
Test for information disclosureIf proxy is enabled, initiate a connection with a short payload and observe if unexpected data appears in the response (this indicates uninitialized stack leakage)Affected if Short payload proxy connections return unexpected data from uninitialized stack memory
You are affected if Exim version is between 4.88 and 4.99.3 inclusive AND proxy configurations that trigger the vulnerable code path with short payloads are active.
Generated from the published advisory. Verify against your own configuration.
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 · scoped4.99.4
Upgrade Exim to version 4.99.4 or later. If immediate upgrading is not feasible, review and modify proxy configurations to avoid the vulnerable code path.
Exim 4.99.4 or latest stable 4.x release
- 1. Check current Exim version: exim -v -bV
- 2. Upgrade Exim to version 4.99.4 or later (e.g., 4.99.4, 4.99.5, or latest stable 4.x release) using your system's package manager (apt, yum, dnf) or compile from source
- 3. Verify the upgrade: exim -bV should show version >= 4.99.4
- 4. Review and restart Exim service: systemctl restart exim or service exim restart
- 5. Test that proxy configurations handle short payloads correctly and no longer leak uninitialized memory
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation2.0 h
- Implementation2.0 h
- Testing3.0 h
- Review / QA1.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,224.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-48840 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-48840 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.
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.
- 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