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CVE-2026-40686

Quick assessment

Affected
Exim Exim
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.

Exim是Exim开源的一个运行于Unix系统中的开源消息传送代理（MTA），它主要负责邮件的路由、转发和投递。 Exim 4.99.2之前版本存在缓冲区错误漏洞，该漏洞源于utf8运算符处理畸形UTF-8标头数据时，存在大UTF-8尾随字符导致的越界读取，可能通过错误消息泄露信息。

CVSS 3.7 · Low EPSS 0.40% · P32

Possible ATT&CK Techniques 1 AI

T1567 · Exfiltration Over Web Service

Affected Version Matrix 1

VendorProduct Version RangeStatus
Exim Exim < 4.99.2 affected
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I. Basic Information for CVE-2026-40686

Vulnerability Information
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Vulnerability Title
N/A
Source: CVE Program / CVE List V5
Vulnerability Description
In Exim before 4.99.2, when utf8 operators are enabled, there is an out-of-bounds read if large UTF-8 trailing characters are present (malformed UTF-8 header data). Information might be divulged within an error message produced during handling of an unrelated e-mail message.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
跨界内存读
Source: CVE Program / CVE List V5
Vulnerability Title
Exim 缓冲区错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Exim是Exim开源的一个运行于Unix系统中的开源消息传送代理（MTA），它主要负责邮件的路由、转发和投递。 Exim 4.99.2之前版本存在缓冲区错误漏洞，该漏洞源于utf8运算符处理畸形UTF-8标头数据时，存在大UTF-8尾随字符导致的越界读取，可能通过错误消息泄露信息。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Exim Exim 0 ~ 4.99.2 -

II. Public POCs for CVE-2026-40686

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III. Intelligence Information for CVE-2026-40686

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Patches & Fixes for CVE-2026-40686 (1)

Mailing List Discussions for CVE-2026-40686 (1)

Other References for CVE-2026-40686 (2)

Other References for CVE-2026-40686 (1)

Same Patch Batch · Exim · 2026-04-30 · 4 CVEs total

CVE-2026-40685 6.5 MEDIUM Exim 缓冲区错误漏洞
CVE-2026-40684 5.9 MEDIUM Exim 安全漏洞
CVE-2026-40687 4.8 MEDIUM Exim 安全漏洞

IV. Related Vulnerabilities

Same product: Exim
Same vendor: Exim
Same weakness: CWE-125

V. Comments for CVE-2026-40686

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