icalendar is an RFC 5545 compatible parser and generator of iCalendar files for Python. From 6.1.0 until 7.2.2, vInt.from_ical accepts an attacker-controlled VALARM REPEAT value and applications that request alarm times can eagerly expand it without an application-level limit. Alarms.times and Alarms.active reach the unbounded expansion in versions starting with 6.1.0, while Alarm.triggers adds a second affected path starting with 7.0.0. Parsing alone does not trigger the issue, but accessing these properties can consume excessive CPU time and heap memory and terminate or stall a service. This issue is fixed in version 7.2.2.
CVE-2026-77399
MEDIUMPre-NVD 6.56.5—Trending — 3 sources updated this week
EchelonGraph scoreMEDIUM confidence
This medium-severity CVE scores 6.5 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.5%, top 55% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).
Triggered by: NVD CVSS baseline
Sources: epss, secondary
6.5EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
- Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 1%CVSS: 6.5Exploit: None knownExposed: 0
No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.
- CVSS v3
- 6.5
- EG Score
- 6.5(medium)
- EG Risk
- 29(Track)EG Risk 29/100SSVC: 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 computedSeverity65% × 45%Exploitation1% × 40%Automatability0% × 15%Action: Routine — remediate on your standard cadence. - EPSS PROB
- 1%
- EPSS %ILE
- 45%
- KEV
- Not listed
Published
September 22, 2026
Last Modified
September 23, 2026
Advisory Details (5)
Auto-updated Sep 22, 2026Patch available. Sources: github_commit, github_release, github, github_pr.
github_release Patch Available
v7.2.2
Patch available: collective/icalendar v7.2.2
https://github.com/collective/icalendar/releases/tag/v7.2.2github_commit Patch Available
commit cddd37226adb (collective/icalendar)
Patch available: collective/icalendar v7.3.0 (contains commit cddd37226adb)
https://github.com/collective/icalendar/commit/cddd37226adbc52cca52a399f61d38a378221219github_commit Patch Available
commit 157f85137c65 (collective/icalendar)
Patch available: collective/icalendar v7.2.1 (contains commit 157f85137c65)
https://github.com/collective/icalendar/commit/157f85137c65565a308bbcf4fdcc7d8ebce01267github_pr Patch Available
Port GHSA-qjcq-q7h7-r74v fix to main
Patch available: collective/icalendar v7.3.0 (PR #1571 merged 2026-07-20)
https://github.com/collective/icalendar/pull/1571github Patch Available
Denial of service via unbounded VALARM REPEAT expansion · Advisory · collective/icalendar · GitHub
Affected: 7.2.2. Expansion is now capped at
https://github.com/collective/icalendar/security/advisories/GHSA-qjcq-q7h7-r74vWeakness Classification(2)
MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.
Data Freshness Timeline
(refreshed 7× in last 7d / 7× 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.
- 2026-09-23 18:25 UTCEG score recompute
- 2026-09-23 17:54 UTCEPSS rescore
- 2026-09-23 15:20 UTCEG score recompute
- 2026-09-23 14:50 UTCEG score recompute
- 2026-09-22 19:37 UTCEG score recompute
- 2026-09-22 19:08 UTCEG score recompute
- 2026-09-22 19:08 UTCMITRE cvelistV5first tracked
Related CVEs(same CWE)
Frequently asked(5)
What is CVE-2026-77399?
CVE-2026-77399 is a medium vulnerability published on September 22, 2026. icalendar is an RFC 5545 compatible parser and generator of iCalendar files for Python. From 6.1.0 until 7.2.2, vInt.from_ical accepts an attacker-controlled VALARM REPEAT value and applications that request alarm times can eagerly expand it without an application-level limit. Alarms.times and…
When was CVE-2026-77399 disclosed?
CVE-2026-77399 was first published in the National Vulnerability Database on September 22, 2026, with the most recent update on September 23, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-77399 actively exploited?
CVE-2026-77399 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 1% probability of exploitation in the next 30 days, which ranks it in the top 55.2% of all scored CVEs.
What is the CVSS score of CVE-2026-77399?
CVE-2026-77399 has a CVSS v3 base score of 6.5 (NVD).
How do I remediate CVE-2026-77399?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-77399, 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-2026-77399
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