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CVE-2026-20355— Cisco Secure Email S/MIME Ciphertext Decryption Vulnerabilty

Quick assessment

Affected
Cisco Cisco Secure Email
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.

Cisco 安全电子邮件（Secure Email）中的安全/多用途互联网邮件扩展（S/MIME）解密功能存在多个漏洞，可能允许未经认证的远程攻击者从加密邮件消息中恢复明文内容。 这些漏洞源于对消息完整性验证不足。攻击者可以通过中间人（man-in-the-middle）技术拦截并篡改邮件网关之间的流量，从而利用这些漏洞。成功利用这些漏洞后，攻击者能够获取加密通信中的明文内容。

CVSS 5.9 · Medium

Possible ATT&CK Techniques 1 AI

T1561 · Disk Wipe

Affected Version Matrix 24

VendorProduct Version RangeStatus
Cisco Cisco Secure Email 14.0.0-698 affected
13.5.1-277 affected
13.0.0-392 affected
14.2.0-620 affected
13.0.5-007 affected
13.5.4-038 affected
14.2.1-020 affected
14.3.0-032 affected
… +16 more rows
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I. Basic Information for CVE-2026-20355

Vulnerability Information
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Vulnerability Title
Cisco Secure Email S/MIME Ciphertext Decryption Vulnerabilty
Source: CVE Program / CVE List V5
Vulnerability Description
Multiple vulnerabilities in the Secure/Multipurpose Internet Mail Extensions (S/MIME) decryption functionality of Cisco Secure Email could allow an unauthenticated, remote attacker to recover plain text from encrypted email messages. These vulnerabilities are due to insufficient validation of message integrity. An attacker could exploit these vulnerabilities by using a machine-in-the-middle technique to intercept and modify traffic between email gateways. A successful exploit could allow the attacker to obtain plaintext content from the encrypted communication.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
对数据真实性的验证不充分
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
Cisco Cisco Secure Email 14.0.0-698 -

II. Public POCs for CVE-2026-20355

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III. Intelligence Information for CVE-2026-20355

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Vendor Advisories for CVE-2026-20355 (1)

Same Patch Batch · Cisco · 2026-09-02 · 11 CVEs total

CVE-2026-20279 9.8 CRITICAL Cisco IOS XR Software Security Hardening Release: September 2026
CVE-2026-20274 9.8 CRITICAL Cisco IOS XR Software Security Hardening Release: September 2026
CVE-2026-20212 9.8 CRITICAL Cisco Nexus 3000 and 9000 Series Switches Silicon One Hardware Abstraction Layer Remote Co
CVE-2026-20280 8.8 HIGH Cisco IOS XR Software Security Hardening Release: September 2026
CVE-2026-20278 8.8 HIGH Cisco IOS XR Software Security Hardening Release: September 2026
CVE-2026-20275 8.8 HIGH Cisco IOS XR Software Security Hardening Release: September 2026
CVE-2026-20276 8.6 HIGH Cisco IOS XR Software Security Hardening Release: September 2026
CVE-2026-20277 8.2 HIGH Cisco IOS XR Software Security Hardening Release: September 2026
CVE-2026-20281 7.5 HIGH Cisco Desk Phone 9800 Series, IP Phone 7800 and 8800 Series, and Video Phone 8875 with SIP
CVE-2026-20354 5.9 MEDIUM Cisco Secure Email S/MIME Ciphertext Decryption Vulnerabilty

IV. Related Vulnerabilities

Same product: Cisco Secure Email
Same vendor: Cisco
Same weakness: CWE-345

V. Comments for CVE-2026-20355

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