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CVE-2026-40203

Quick assessment

Affected
Open-Xchange GmbH OX Dovecot Pro
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.

当启用 IMAP 压缩时，同一个会话中的压缩状态会在多次响应之间复用，因此响应的大小不仅取决于攻击者提供的邮件，还取决于同一邮箱中其他邮件。一个能够向某用户发送邮件并同时观察该用户 IMAP 流量大小的攻击者，可以确认一条小型邮件的正文是否与某个猜测的文本相匹配。虽然尚未证明可以恢复任意未知内容，但该攻击可以披露某条类似机密信息的邮件正文是否与某个候选文本一致。建议禁用 IMAP 压缩。更新至不受影响的版本。目前没有公开的可用漏洞利用案例。

CVSS 3.7 · Low
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I. Basic Information for CVE-2026-40203

Vulnerability Information
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Vulnerability Title
N/A
Source: CVE Program / CVE List V5
Vulnerability Description
When IMAP compression is enabled, the same compression state is reused across responses in a session, so response sizes depend on both attacker-supplied mail and other mail in the same mailbox. An attacker that can send mail to a user and can also observe the sizes of that user's IMAP traffic can confirm whether the body of a small message matches a guessed text. Recovery of arbitrary unknown content was not demonstrated, but the attack can disclose whether a secret-like message body matches a candidate. Disable IMAP compression. Update to non-vulnerable version. No publicly available exploits are known.
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
信息暴露
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
Open-Xchange GmbH OX Dovecot Pro 2.3.0 ~ 2.3.22.2 -
Open-Xchange GmbH OX Dovecot CE 2.3.0 ~ 2.4.5 -

II. Public POCs for CVE-2026-40203

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III. Intelligence Information for CVE-2026-40203

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Same Patch Batch · Open-Xchange GmbH · 2026-08-28 · 25 CVEs total

CVE-2026-42007 9.1 CRITICAL OpenWebmail 6.0 及之前版本 内存越界写漏洞
CVE-2026-42391 7.5 HIGH IMAP未认证ID命令引发内存与CPU资源耗尽
CVE-2026-33605 7.5 HIGH ManageSieve 认证前畸形命令崩溃DoS漏洞
CVE-2026-27852 7.5 HIGH Dovecot 特定版本 IMAP 邮件解析内存耗尽 DoS
CVE-2026-73208 7.4 HIGH Dovecot OAuth2 audience 冒充 scope 导致越权
CVE-2026-40018 7.4 HIGH 未知软件：无已知公开利用
CVE-2026-73209 6.5 MEDIUM IMAP服务栈溢出拒绝服务漏洞
CVE-2026-40017 6.5 MEDIUM Dovecot特定版本IMAP THREAD命令哈希碰撞DoS漏洞
CVE-2026-40014 6.5 MEDIUM IMAP THREAD命令致高CPU占用，修复指定版本
CVE-2026-52687 6.5 MEDIUM Dovecot IMAP压缩算法致拒绝服务
CVE-2026-33604 5.9 MEDIUM Dovecot SMTP邮件走私漏洞
CVE-2026-40019 5.9 MEDIUM ManageSieve 0.6.1 存在 CPU 耗尽型拒绝服务漏洞
CVE-2026-40205 5.9 MEDIUM OAuth2 令牌校验缺陷，远程验证未强制作用域
CVE-2026-33606 4.8 MEDIUM Dovecot dsync流协议邮件内容注入漏洞
CVE-2026-33263 4.3 MEDIUM 提交登录模块崩溃：高并发下连接上限触发 epoll 异常
CVE-2026-42395 4.3 MEDIUM OpenSSH可信代理NUL字节致登录进程崩溃
CVE-2026-33607 4.3 MEDIUM IMAP LIST命令致CPU耗尽或DoS
CVE-2026-40015 4.3 MEDIUM IMAP-hibernate越界读致进程崩溃
CVE-2026-40013 4.3 MEDIUM ManageSieve 越界写导致拒绝服务漏洞
CVE-2026-42392 4.3 MEDIUM 该漏洞影响某软件的IMAP URLAUTH功能，版本未知，类型为信息泄露

Showing top 20 of 25 CVEs. View all on vendor page → →

IV. Related Vulnerabilities

Same product: OX Dovecot Pro
Same vendor: Open-Xchange GmbH
Same weakness: CWE-200

V. Comments for CVE-2026-40203

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