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.
CVE-2026-40203
LOWPre-NVD 3.73.7—Trending — 4 sources updated this week
EchelonGraph scoreHIGH confidence
Score 3.7 from GitHub Security Advisory (severity: LOW) published 2026-08-28. a secondary CVSS source baseline 3.7; sources differ by 0.0.
Triggered by: GitHub Security Advisory CVSS
Sources: ghsa, secondary
3.7EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
- Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 3.7Exploit: None knownExposed: 0
No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.
- CVSS v3
- 3.7
- EG Score
- 3.7(high)
- EG Risk
- 17(Track)EG Risk 17/100SSVC: 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 computedSeverity37% × 45%Exploitation0% × 40%Automatability0% × 15%Action: Routine — remediate on your standard cadence. - EPSS PROB
- 0%
- EPSS %ILE
- 12%
- KEV
- Not listed
Published
August 28, 2026
Last Modified
August 28, 2026
References (1)
Vendor Advisories for CVE-2026-40203(1)
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 8× in last 7d / 8× 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.
- 2026-08-30 01:22 UTCEPSS rescore
- 2026-08-28 16:36 UTCEG score recompute
- 2026-08-28 16:36 UTCGHSA enrichment
- 2026-08-28 15:39 UTCEG score recompute
- 2026-08-28 15:38 UTCGHSA enrichment
- 2026-08-28 12:23 UTCEG score recompute
- 2026-08-28 11:25 UTCEG score recompute
- 2026-08-28 11:19 UTCMITRE cvelistV5first tracked
Related CVEs(same CWE)
Frequently asked(5)
What is CVE-2026-40203?
CVE-2026-40203 is a low vulnerability published on August 28, 2026. 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…
When was CVE-2026-40203 disclosed?
CVE-2026-40203 was first published in the National Vulnerability Database on August 28, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-40203 actively exploited?
CVE-2026-40203 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 87.8% of all scored CVEs.
What is the CVSS score of CVE-2026-40203?
CVE-2026-40203 has a CVSS v3 base score of 3.7 (NVD).
How do I remediate CVE-2026-40203?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-40203, 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-2026-40203
Is Your Infrastructure Affected by CVE-2026-40203?
EchelonGraph automatically scans your cloud infrastructure and maps CVE exposure using blast radius analysis.