Which versions of SmarterMail are affected by CVE-2026-40514?

Organizations running SmarterMail versions before build 9610 face direct risk of email compromise and data theft through a vulnerability in the sharing-token mechanism (CVE-2026-40514).. A patch is available.

How to fix or mitigate CVE-2026-40514?

Within 24 hours, conduct an inventory of all SmarterMail systems and document their current build versions. Within 7 days, test SmarterMail build 9610 or later in a non-production environment, validating email sharing, attachment handling, and file storage operations. Within 30 days, deploy the patched version to all production systems and confirm remediation is complete.

SmarterMail CVE-2026-40514

Q: What is the CVSS score of CVE-2026-40514?

CVE-2026-40514 has a CVSS 4.0 base score of 8.2 (High). CVSS vector: CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X. EPSS exploitation probability: 0.0%.

EUVD-2026-25856 HIGH

Use of Cryptographically Weak Pseudo-Random Number Generator (PRNG) (CWE-338)

2026-04-27 VulnCheck

Information Disclosure Oracle Smartermail

8.2

CVSS 4.0 · NVD

Severity by source

NVD PRIMARY

8.2 HIGH

CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

vuln.today AI

5.9 MEDIUM

Network-reachable and unauthenticated (AV:N/PR:N), but AC:H for the multi-request seed brute force via the oracle; confidentiality-only (C:H, I:N/A:N) since content is read, not altered.

3.1 AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

4.0 AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

Primary rating from NVD.

CVSS VectorNVD

Attack Vector

Network

Attack Complexity

High

Privileges Required

None

User Interaction

None

Scope

Lifecycle Timeline

Analysis Generated

Jul 24, 2026 - 01:58 vuln.today

Severity Changed

Apr 27, 2026 - 15:22 NVD

MEDIUM HIGH

CVSS changed

Apr 27, 2026 - 15:22 NVD

5.9 (MEDIUM) 8.2 (HIGH)

EUVD ID Assigned

Apr 27, 2026 - 15:00 euvd

EUVD-2026-25856

Patch released

Apr 27, 2026 - 15:00 nvd

Patch available

CVE Published

Apr 27, 2026 - 14:21 nvd

HIGH 8.2

DescriptionCVE.org

SmarterTools SmarterMail builds prior to 9610 contain a cryptographic weakness in the file and email sharing endpoints that use DES-CBC encryption with keys and initialization vectors derived from System.Random seeded with insufficient entropy, reducing the seed space to approximately 19,000 possible values. An unauthenticated attacker can use the attachment download endpoint as an oracle to determine the seed in use and derive encryption keys and initialization vectors to forge sharing tokens for arbitrary emails, attachments, or file storage contents without prior access to the targeted content.

AnalysisAI

Sharing-token forgery in SmarterTools SmarterMail builds before 9610 lets remote unauthenticated attackers decrypt and access arbitrary emails, attachments, and file-storage contents. The file/email sharing endpoints protect tokens with DES-CBC keys and IVs derived from System.Random seeded with only ~19,000 possible values, and the attachment download endpoint leaks enough information to act as an oracle for recovering the seed. No public exploit is identified at time of analysis, and EPSS is low (0.03%), consistent with the high-complexity, non-automatable oracle attack it requires.

Technical ContextAI

SmarterMail is a Windows/.NET commercial mail server and collaboration platform. The flaw is a CWE-338 (use of a cryptographically weak PRNG) issue: sharing tokens are encrypted with DES - itself a deprecated 56-bit block cipher - in CBC mode, but the real weakness is that the symmetric key and initialization vector are generated from .NET's System.Random, a non-cryptographic linear PRNG. Because System.Random is seeded with insufficient entropy, the effective seed space collapses to roughly 19,000 candidates. Since the same seed determines both key and IV for every sharing token, recovering the seed reconstructs the full keystream material, and the unauthenticated attachment download endpoint returns behavior that distinguishes correct from incorrect seed guesses, functioning as a decryption/validation oracle. The single affected CPE is cpe:2.3:a:smartertools_inc.:smartermail:*.

RemediationAI

Vendor-released patch: build 9610 (version 100.0.9610) - upgrade every SmarterMail instance to build 9610 or later per the SmarterTools release notes (https://www.smartertools.com/smartermail/release-notes/current). Until the upgrade is applied, reduce exposure by restricting reachability of the file/email sharing and attachment download endpoints: place the server behind a VPN or IP allowlist, or use a reverse proxy/WAF to block or rate-limit unauthenticated access to the attachment download endpoint that serves as the oracle, which raises the cost of the seed brute force at the expense of legitimate anonymous share-link access. Disabling public file/email sharing where it is not required removes the vulnerable token path entirely but breaks external sharing workflows. These are compensating controls only; because the root cause is weak key/IV generation, patching to build 9610 is the sole complete fix. Refer to the VulnCheck advisory (https://www.vulncheck.com/advisories/smartertools-smartermail-build-9610-cryptographic-weakness-via-weak-rng) for details.