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CVE-2026-107582— Inefficient Algorithmic Complexity 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.

hMailServer（版本 6.3.3 至 6.3.5）的 REST API 以及 IMAP PREVIEW（预览）响应存在算法复杂度低效问题。远程未经身份验证的攻击者可通过发送特定消息，导致 Web 邮件、管理控制台和 REST API 不可用。 为了在文件夹的消息列表中显示每条消息的摘要片段，服务器会对包含 HTML 部分但无纯文本部分的消息进行解码。该过程使用字符串替换操作处理字符实体引用，其计算复杂度与实体引用数量的平方成正比。因此，当收到一条包含大量字符实体引用的纯 HTML 消息时，每当收件人查看该文

CVSS 6.5 · Medium

Possible ATT&CK Techniques 1 AI

T1499 · Endpoint Denial of Service
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I. Basic Information for CVE-2026-107582

Vulnerability Information
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Vulnerability Title
Inefficient Algorithmic Complexity in hMailServer
Source: CVE Program / CVE List V5
Vulnerability Description
Inefficient algorithmic complexity in the REST API (6.3.3 through 6.3.5) and the IMAP PREVIEW response (6.2.22 through 6.3.5) of Progressive Robot hMailServer allows a remote unauthenticated attacker to make the webmail, the administration console and the REST API unavailable by sending a message. To show a snippet of each message in a folder's message list, the server decoded the character entity references of a message that has an HTML part and no text part with a string replacement whose work grew with the square of their number. A received HTML-only message holding a very large number of entity references therefore keeps one of the listener's four worker threads busy for minutes or longer each time the recipient's webmail lists the folder, without the message being opened, so that a few such listings leave the HTTP listener unable to answer anybody. The IMAP PREVIEW response read such text the same way, holding an IMAP thread for each client that asks for the preview of such a message. The flaw is in the server's shared string class, whose replace and remove both ran in quadratic time.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
算法复杂性
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
Progressive Robot Ltd hMailServer 6.2.22-pre1 ~ 6.3.6 -

II. Public POCs for CVE-2026-107582

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III. Intelligence Information for CVE-2026-107582

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Other References for CVE-2026-107582 (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-2026-104660 7.8 HIGH Missing Authorization in hMailServer
CVE-2026-104658 7.8 HIGH Reliance on Untrusted Inputs in a Security Decision in hMailServer
CVE-2026-107573 7.8 HIGH Incorrect Default Permissions 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-2026-104659 7.5 HIGH Origin Validation Error 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-2026-104704 7.4 HIGH Cleartext Transmission of Sensitive Information in hMailServer
CVE-2026-107578 6.7 MEDIUM Improper Link Resolution Before File Access ('Link Following') in hMailServer
CVE-2026-107583 6.5 MEDIUM Inefficient Algorithmic Complexity 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-2026-107580 6.5 MEDIUM Inefficient Algorithmic Complexity in hMailServer
CVE-2026-103011 6.5 MEDIUM Heap-based Buffer Overflow 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-407

V. Comments for CVE-2026-107582

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