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CVE-2026-104704— Cleartext Transmission of Sensitive Information in hMailServer

Quick assessment

Affected
Progressive Robot Ltd hMailServer
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Progressive Robot hMailServer 6.0.0 至 6.3.5 版本在通过 DNSSEC 验证的 TLSA 记录不包含 DANE-EE（usage 3）记录时，未对发往对应邮件交换器（MX）的出站 SMTP 传输强制启用 TLS，这与 RFC 7672 第 2.2 节的要求相悖。该服务器仅接受 DANE-EE 记录，并将经过 DNSSEC 验证但仅包含 DANE-TA（usage 2）或其他不可用记录的 TLSA 记录集视为“未发布任何记录”，导致发往此类主机的邮件回退到使用 Opportu

CVSS 7.4 · High

Possible ATT&CK Techniques 1 AI

T1557 · Adversary-in-the-Middle
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I. Basic Information for CVE-2026-104704

Vulnerability Information
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Vulnerability Title
Cleartext Transmission of Sensitive Information in hMailServer
Source: CVE Program / CVE List V5
Vulnerability Description
Progressive Robot hMailServer 6.0.0 through 6.3.5 does not enforce TLS for outbound SMTP delivery to a mail exchanger whose DNSSEC-validated TLSA records contain no DANE-EE (usage 3) record, contrary to RFC 7672 section 2.2. The server used only DANE-EE records and treated a validated TLSA record set consisting of DANE-TA (usage 2) or otherwise unusable records as if no records were published, so delivery to such a host fell back to opportunistic TLS. An attacker with an active position on the network path between the server and the recipient's mail exchanger can suppress or break the STARTTLS negotiation and cause messages to be delivered in cleartext, where they can be read and modified.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
敏感数据的明文传输
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
Progressive Robot Ltd hMailServer 6.0.0 ~ 6.3.6 -

II. Public POCs for CVE-2026-104704

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III. Intelligence Information for CVE-2026-104704

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Other References for CVE-2026-104704 (2)

Same Patch Batch · Progressive Robot Ltd · 2026-10-08 · 22 CVEs total

CVE-2026-103647 8.0 HIGH Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') in hM
CVE-2026-103010 7.8 HIGH Heap-based Buffer Overflow in hMailServer
CVE-2026-107573 7.8 HIGH Incorrect Default Permissions in hMailServer
CVE-2026-104658 7.8 HIGH Reliance on Untrusted Inputs in a Security Decision in hMailServer
CVE-2026-104660 7.8 HIGH Missing Authorization in hMailServer
CVE-2026-104659 7.5 HIGH Origin Validation Error in hMailServer
CVE-2026-107577 7.5 HIGH Loop with Unreachable Exit Condition ('Infinite Loop') in hMailServer
CVE-2026-107574 7.5 HIGH Inefficient Algorithmic Complexity in hMailServer
CVE-2026-107579 7.5 HIGH Inefficient Algorithmic Complexity in hMailServer
CVE-2026-107576 7.5 HIGH Inefficient Algorithmic Complexity in hMailServer
CVE-2026-103649 7.5 HIGH Synchronous Access of Remote Resource without Timeout in hMailServer
CVE-2026-107584 7.4 HIGH Not Failing Securely ('Failing Open') in hMailServer
CVE-2026-107578 6.7 MEDIUM Improper Link Resolution Before File Access ('Link Following') in hMailServer
CVE-2026-103011 6.5 MEDIUM Heap-based Buffer Overflow in hMailServer
CVE-2026-107572 6.5 MEDIUM Inefficient Regular Expression Complexity in hMailServer
CVE-2026-107581 6.5 MEDIUM Inefficient Algorithmic Complexity in hMailServer
CVE-2026-107582 6.5 MEDIUM Inefficient Algorithmic Complexity in hMailServer
CVE-2026-107580 6.5 MEDIUM Inefficient Algorithmic Complexity in hMailServer
CVE-2026-107583 6.5 MEDIUM Inefficient Algorithmic Complexity in hMailServer
CVE-2026-107587 5.9 MEDIUM Improper Certificate Validation in hMailServer

Showing top 20 of 22 CVEs. View all on vendor page → →

IV. Related Vulnerabilities

Same product: hMailServer
Same vendor: Progressive Robot Ltd
Same weakness: CWE-319

V. Comments for CVE-2026-104704

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