HOMEVULNERABILITIESCVE-2026-40685
CRITICAL

CVE-2026-40685

CWE-684Published: April 30, 2026· Updated: May 1, 2026

9.8
CVSS v3.1
EPSS:0.05%probability of exploitation in 30 daysPercentile:16.6th

Official Description

In Exim before 4.99.2, when JSON lookup is enabled, an out-of-bounds heap write can occur when a JSON operator encounters malformed JSON in an untrusted header, because of an incorrect implementation of \ skipping.

NVD Source

Technical Analysis

CVE-2026-40685 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.

A successful exploit results in complete confidentiality breach (data exposure), full integrity compromise (data manipulation), availability disruption (denial of service), with a CVSS base score of 9.8.

CVSS v3.1 Vector Breakdown

Exploitability
Attack VectorNetwork
Attack ComplexityLow
Privileges Req.None
User InteractionNone
ScopeUnchanged
Impact
ConfidentialityHigh
IntegrityHigh
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected Vendors & Products

exim1 product
exim
Source: NVD CPE · 1 total CPE entries

Exploit & PoC Resources

NO KNOWN EXPLOITNo public exploit confirmed at this time
Exploit-DB
Offensive Security exploit database
GitHub PoC Search
Community PoC repositories
Rapid7 / Metasploit
Metasploit module search
PacketStorm
Security advisories & exploits
NVD Detail
Official NIST entry
MITRE CVE
CVE Program entry
External links open in a new tab. Always verify in a controlled environment before use.

Official Patches & Advisories

PATCHhttps://code.exim.org/exim/exim/commit/9fdc057e71b87c87a0d3d2288b2810a0efaaba57
ADVISORYhttps://exim.org/static/doc/security/cve-2026-04.1/CVE2026-40685.assessment
ADVISORYhttps://www.openwall.com/lists/oss-security/2026/04/30/21

All References (4)

→
https://code.exim.org/exim/exim/commit/9fdc057e71b87c87a0d3d2288b2810a0efaaba57Patch
→
https://exim.org/static/doc/security/CVE-2026-40685.txtBroken Link
→
https://exim.org/static/doc/security/cve-2026-04.1/CVE2026-40685.assessmentVendor Advisory
→
https://www.openwall.com/lists/oss-security/2026/04/30/21Mailing List · Third Party Advisory

Quick Facts

CVE IDCVE-2026-40685
CVSS Score9.8 / 10
SeverityCRITICAL
WeaknessCWE-684
CISA KEVNo
EPSS (30d)0.05%
Affected1 vendor
PublishedApr 30, 2026

Related CVEs (CWE-684)

CVE-2026-44597
9.1
CVE-2026-40684
7.5
CVE-2026-42255
6.5
CVE-2026-35379
3.3
CVE-2026-35381
3.3

Recommended Actions

  • →Apply vendor patches immediately
  • →Monitor CVE-2026-40685 in threat intel feeds
  • →Review IDS/IPS signatures for exploitation attempts
Data sourced from NVD (NIST), CISA KEV, and EPSS (FIRST). Analysis generated by CTIWATCH.COM. CVE data is provided under the NVD usage policy.
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