EUVD-2026-94865
GHSA-j6xf-vpp5-5357
Severity by source
AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:L/A:N
Unauthenticated remote delivery (AV:N/PR:N) but multiple preconditions and separate ciphertext capture give AC:H; victim must open the signed message (UI:R); confidentiality of encrypted mail is high while certificate-store poisoning is a low integrity impact.
Primary rating from Vendor (GitLab).
CVSS VectorVendor: GitLab
Lifecycle Timeline
2DescriptionCVE.org
Improper certificate validation in the webmail of Progressive Robot hMailServer 6.3.2 through 6.3.5 allows a remote unauthenticated attacker to have S/MIME-encrypted mail that the account later sends to another correspondent also encrypted to the attacker's key. When its recipient opened a signed message, the webmail kept the signer's certificate for encrypting replies whether or not the server found its chain trusted, under the first e-mail address the certificate listed rather than the message's From address, and beside any certificate already held for that address. Encrypted mail later sent from the webmail to that address was encrypted to every certificate held for it, so a holder of the kept certificate's key who obtains a copy of such a message can read it.
AnalysisAI
Improper certificate validation in the hMailServer webmail S/MIME handler (versions 6.3.2 through 6.3.5) allows a remote unauthenticated attacker to have their own encryption key silently added to the recipient set of messages a victim later sends to a target correspondent, exposing those messages to anyone holding the attacker's private key. The webmail keeps the signing certificate from any opened S/MIME-signed message even when the server finds the chain untrusted, stores it under the certificate's first listed e-mail address rather than the message's From address, and appends it alongside any legitimate certificate already held for that address; the attacker still needs to independently obtain a copy of the later ciphertext (for example through mailbox or network interception) to decrypt it. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires that the hMailServer webmail S/MIME feature be in active use and that a webmail user open an attacker-supplied S/MIME-signed message whose signing certificate lists the targeted correspondent's email address as its first listed address - the webmail then stores that certificate (even with an untrusted/unverified chain) keyed to the listed address rather than the message's From address, and alongside any legitimate certificate already held. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | This is a moderate-priority confidentiality flaw, not an urgent fire. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | Full exploit scenario with step-by-step reproduction available after sign-in. |
| Remediation | Upgrade to hMailServer 6.3.6, which is the vendor-released fix for CVE-2026-107587 (release notes: https://gitlab.com/hmailserver/hmailserver/-/releases/v6.3.6, work item: https://gitlab.com/hmailserver/hmailserver/-/work_items/66); this is the only complete remediation because the corrected behavior involves both chain-trust enforcement and correct binding of retained certificates to the message From address without merging into the existing certificate store. … Detailed patch versions, workarounds, and compensating controls in full report. |
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External POC / Exploit Code
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