CVE-2026-20355

MEDIUMPre-NVD 5.95.9—
EchelonGraph scoreHIGH confidence

Score 5.9 from GitHub Security Advisory published 2026-09-02. the CNA's CVSS baseline 5.9; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: cna:cisco, epss, ghsa
Trending — 3 sources updated this week
5.9EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 5.9Exploit: None knownExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

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.

CVSS v3
5.9
EG Score
5.9(high)
EG Risk
27(Track)
EG Risk 27/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity59% × 45%
Exploitation0% × 40%
Automatability0% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
4%
KEV
Not listed

Published

September 2, 2026

Last Modified

September 8, 2026

Advisory Details (1)

Auto-updated Sep 2, 2026
No patch confirmed yet.
generic

Cisco Secure Email Secure/Multipurpose Internet Mail Extensions Ciphertext Decryption Vulnerabilities

https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-esa-smime-disc-dzw4rEdY

Vendor Advisories for CVE-2026-20355(2)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 19× in last 7d / 30× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-09-11 14:52 UTCEPSS rescore
  2. 2026-09-11 12:53 UTCEG score recompute
  3. 2026-09-11 12:53 UTCGHSA enrichment
  4. 2026-09-10 14:09 UTCEG score recompute
  5. 2026-09-10 14:09 UTCGHSA enrichment
  6. 2026-09-10 09:34 UTCEPSS rescore
  7. 2026-09-09 15:37 UTCEG score recompute
  8. 2026-09-09 15:37 UTCGHSA enrichment
  9. 2026-09-08 22:00 UTCEPSS rescore
  10. 2026-09-08 17:05 UTCEG score recompute
  11. 2026-09-08 17:05 UTCGHSA enrichment
  12. 2026-09-08 10:59 UTCEG score recompute
  13. 2026-09-08 10:59 UTCGHSA enrichment
  14. 2026-09-07 16:01 UTCEPSS rescore
  15. 2026-09-07 12:18 UTCEG score recompute
  16. 2026-09-07 12:17 UTCGHSA enrichment
  17. 2026-09-06 13:47 UTCEPSS rescore
  18. 2026-09-06 13:43 UTCGHSA enrichment
  19. 2026-09-05 15:11 UTCGHSA enrichment
  20. 2026-09-04 16:39 UTCEG score recompute
  21. 2026-09-04 16:39 UTCGHSA enrichment
  22. 2026-09-04 05:06 UTCEPSS rescore
  23. 2026-09-03 18:06 UTCGHSA enrichment
  24. 2026-09-02 19:31 UTCGHSA enrichment
  25. 2026-09-02 18:36 UTCEG score recompute
Show 5 more
  1. 2026-09-02 18:36 UTCGHSA enrichment
  2. 2026-09-02 18:05 UTCEG score recompute
  3. 2026-09-02 17:35 UTCEG score recompute
  4. 2026-09-02 16:33 UTCEG score recompute
  5. 2026-09-02 16:31 UTCMITRE cvelistV5first tracked

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2026-20355?
CVE-2026-20355 is a medium vulnerability published on September 2, 2026. 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…
When was CVE-2026-20355 disclosed?
CVE-2026-20355 was first published in the National Vulnerability Database on September 2, 2026, with the most recent update on September 8, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-20355 actively exploited?
CVE-2026-20355 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 95.6% of all scored CVEs.
What is the CVSS score of CVE-2026-20355?
CVE-2026-20355 has a CVSS v4.0 base score of 5.9 (CNA self-assessment; NVD's own analysis pending).
How do I remediate CVE-2026-20355?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-20355, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

Explore the affected products and dependency analysis for CVE-2026-20355

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