CVE-2026-40514 is a cryptographic weakness in SmarterTools SmarterMail, scored CVSS 5.9 by NVD. Builds before 9610 derive sharing token keys from a weakly seeded random generator, so tokens can be forged. Update to build 9610 or later, and ideally the current build.
What's affected
- Affected: SmarterMail builds before 9610
- Fixed: build 9610 or later per the record
The record says the file and email sharing endpoints use DES-CBC encryption with keys and initialization vectors derived from System.Random seeded with too little entropy, leaving about 19,000 possible seed values. The attachment download endpoint can act as an oracle to find the seed.
VulnCheck scores the same flaw 8.2 under CVSS 4.0 and credits Maximilian Wiegand of CODE WHITE GmbH. The SmarterMail release notes page lists newer builds than 9610, so you can move past it.
How to check if you're exposed
Find your build number in the SmarterMail admin interface under the About or Settings area, and compare it with 9610. Then review sharing activity. Look at shared links and file storage shares that exist, and check server logs for repeated requests to the attachment download endpoint from one source.
What to do now
- Update SmarterMail to the current build, which is above 9610.
- Review active shares and remove ones you do not need.
- Watch for bursts of failed attachment download requests and rate limit them at your proxy.
- Read the release notes for other security changes in the builds you skipped.
Why it matters
The weakness is CWE-338, use of a cryptographically weak pseudo random number generator. Keys must come from a source an outsider cannot predict. A general purpose random class seeded from a small space shrinks the work needed to roughly a small brute force, which is why about 19,000 possibilities is the key number here.
The NVD score is medium because the attack complexity is high, and the effect is confidentiality loss. Mail systems hold sensitive material, so treat it as more than a routine patch. The record does not flag exploitation in the wild.
Quick check
Why do two scores exist?
NVD uses CVSS 3.1 and lists 5.9. VulnCheck lists 8.2 under CVSS 4.0. The formulas differ, so the numbers differ.
Sources
Last reviewed: 19 October 2026.
