CVE-2026-77399

Description

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.

Overview

State: PUBLISHED
Assigner (CNA): GitHub_M
CVSS severity: MEDIUM
CVSS score: 6.5 / 10
CVSS vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Effective score: 6.5 / 10 MEDIUM source: CNA overview
CWE(s): CWE-400, CWE-834
Reserved: 2026-08-20
Published: 2026-09-22 18:58 UTC
Last updated: 2026-09-22 18:58 UTC
Source: https://raw.githubusercontent.com/CVEProject/cvelistV5/main/cves/2026/77xxx/CVE-2026-77399.json

NVD triage scoring NVD CVE 2.0

Layer NVD adds on top of the CNA's CVE record — published / last-modified timestamps, exploitability / impact subscores, and the FIRST.org EPSS probability that this CVE will be exploited in the wild in the next 30 days.

NVD published: 2026-09-22 19:16:51 UTC
NVD last modified: 2026-09-22 19:16:51 UTC
NVD CVSS v3.1: 6.5 / 10 MEDIUM source: security-advisories@github.com
NVD CVSS vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Exploitability subscore: 2.8 / 10
Impact subscore: 3.6 / 10

European Union Vulnerability Database ENISA EUVD

ENISA's official EU repository for curated vulnerability intelligence. Carries a separate identifier (EUVD-YYYY-NNNN) and frequently exposes an earlier-published description + CVSS than NVD does.

EUVD ID: EUVD-2026-84800
Assigner: GitHub_M
Published: Sep 22, 2026, 6:58:56 PM
Updated: Sep 22, 2026, 6:58:56 PM
EUVD base score (CVSS 3.1): 6.5 / 10
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
EUVD-reported EPSS: 0.0000
Vendors: collective
Products: icalendar (6.1.0, < 7.2.2)

ENISA description: 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.

EUVD references (5)

Affected products (1)

Vendor	Product	Versions	Platforms
collective	icalendar	`>= 6.1.0, < 7.2.2` (affected)	—

Vendor references (5)

References embedded in the original CVE record by the assigning CNA.

https://github.com/collective/icalendar/security/advisories/GHSA-qjcq-q7h7-r74v x_refsource_CONFIRM
https://github.com/collective/icalendar/pull/1571 x_refsource_MISC
https://github.com/collective/icalendar/commit/157f85137c65565a308bbcf4fdcc7d8ebce01267 x_refsource_MISC
https://github.com/collective/icalendar/commit/cddd37226adbc52cca52a399f61d38a378221219 x_refsource_MISC
https://github.com/collective/icalendar/releases/tag/v7.2.2 x_refsource_MISC

Web references (0)

DuckDuckGo results ranked by threat-intel / vendor advisory domains. Generated by the 🔎 Find references (web) button above — same flow as the Remediations search.

No web references attached yet.

NVD-tagged references (5)

Reference list NVD curates from the CNA record, vendor advisories, and third-party reports. The tag chips below are NVD's analyst-assigned categories.

https://github.com/collective/icalendar/commit/157f85137c65565a308bbcf4fdcc7d8ebce01267 security-advisories@github.com
https://github.com/collective/icalendar/commit/cddd37226adbc52cca52a399f61d38a378221219 security-advisories@github.com
https://github.com/collective/icalendar/pull/1571 security-advisories@github.com
https://github.com/collective/icalendar/releases/tag/v7.2.2 security-advisories@github.com
https://github.com/collective/icalendar/security/advisories/GHSA-qjcq-q7h7-r74v security-advisories@github.com

Remediations (10)

CVE-2026-67399 | CVE Details | Armis

web:cve.armis.com

CVE - 2026 -67399 (None). Published 2026 . An unauthenticated remote attacker can deserialize attacker-controlled data in WHMCS (a web hosting billing and automati…

2026-09-23 15:44 UTC
CVE-2026-77399 - icalendar: Denial of service via unbounded VALARM ...

web:cvefeed.io

The following list is the news that have been mention CVE-2026-77399 vulnerability anywhere in the article. Results are limited to the first 20 news articles due to potential performance issues. The following table lists the changes that have been made to the CVE-2026-77399 vulnerability over time.

2026-09-23 15:44 UTC
CVE-2026-77399 - Exploits & Severity - Feedly

web:feedly.com

CVE ID : CVE-2026-77399 Published : Sept. 22, 2026 , 6:58 p.m. 16 minutes ago Description : icalendar is an RFC 5545 compatible parser and generator of iCalendar files for Python.

2026-09-23 15:44 UTC
CVE-2026-67399 - WHMCS Security Update 2026-09-03 | Other | Guides ...

web:help.whmcs.com

A security vulnerability ( CVE - 2026 -67399) has been identified in WHMCS 8.0.x and later involving the submission of forged payloads without adequate restrictions. Under specific conditions, an attacker could use this submission to achieve remote code execution on the server. This issue was responsibly disclosed through our security program and is currently being addressed.

2026-09-23 15:44 UTC
WHMCS Patches Critical Unauthenticated RCE (CVE-2026-67399) — Update to ...

web:hostingdailynews.com

Once a vulnerability is publicly disclosed and a fix becomes available, attackers can analyze the changes between vulnerable and patched versions to develop working exploits. The WHMCS disclosure also comes less than a month after the cPanel authentication vulnerability, CVE - 2026 -41940, reported in August.

2026-09-23 15:44 UTC
Critical WHMCS Security Update Patches RCE Flaws

web:securityonline.info

Patch and Mitigation Steps Administrators must apply the WHMCS security update immediately. The vendor released WHMCS 9.0.8 and 8.13.7 to fix both issues. Read the official CVE - 2026 -67399 advisory for RCE details. Also, review the CVE - 2026 -67398 advisory for the data leak fix .

2026-09-23 15:44 UTC
March 10, 2026—Hotpatch KB5079420 (OS Builds 26200.7979 and 26100.7979 ...

web:support.microsoft.com

This Hotpatch update for Windows 11, version 25H2 and 24H2 (KB5079420), improves functionality, performance, and reliability. To learn more about differences between security updates, optional non-security preview updates, out-of-band (OOB) updates, and continuous innovation, see Windows monthly updates explained. For information on Windows update terminology, see the different types of ...

2026-09-23 15:44 UTC
SAP Security Patch Day - June 2026

web:support.sap.com

SAP security Patch Day Bulletin This post shares the information on security notes that remediate vulnerabilities discovered in SAP products. SAP strongly recommends that the customer visits the support portal and applies patches on priority to protect their SAP landscape. On 9th of June 2026 , SAP security patch day saw the release of 15 new security notes.

2026-09-23 15:44 UTC
SAP Security Patch Day - September 2026

web:support.sap.com

SAP Security Patch Day Bulletin This post shares the information on security notes that remediate vulnerabilities discovered in SAP products. SAP strongly recommends that the customer visits the support portal and applies patches on priority to protect their SAP landscape. On 8 th of September 2026 , SAP security patch day saw the release of 19 new security notes. There is 1 update to ...

2026-09-23 15:44 UTC
Oracle Critical Patch Update Advisory - July 2026

web:www.oracle.com

This Critical Patch Update contains 1448 new security patches across the product families listed below. Please note that a My Oracle Support (MOS) note summarizing the content of this Critical Patch Update and other Oracle Software Security Assurance activities is located at July 2026 Critical Patch Update: Executive Summary and Analysis.

2026-09-23 15:44 UTC

AI Forensic Analysis

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Raw JSON

The full cvelistV5 record. Download as CVE-2026-77399.json.

{
  "containers": {
    "cna": {
      "affected": [
        {
          "product": "icalendar",
          "vendor": "collective",
          "versions": [
            {
              "status": "affected",
              "version": ">= 6.1.0, < 7.2.2"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "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."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "LOW",
            "attackVector": "NETWORK",
            "availabilityImpact": "HIGH",
            "baseScore": 6.5,
            "baseSeverity": "MEDIUM",
            "confidentialityImpact": "NONE",
            "integrityImpact": "NONE",
            "privilegesRequired": "LOW",
            "scope": "UNCHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
            "version": "3.1"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-400",
              "description": "CWE-400: Uncontrolled Resource Consumption",
              "lang": "en",
              "type": "CWE"
            }
          ]
        },
        {
          "descriptions": [
            {
              "cweId": "CWE-834",
              "description": "CWE-834: Excessive Iteration",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-09-22T18:58:56.647Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/collective/icalendar/security/advisories/GHSA-qjcq-q7h7-r74v",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/collective/icalendar/security/advisories/GHSA-qjcq-q7h7-r74v"
        },
        {
          "name": "https://github.com/collective/icalendar/pull/1571",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/collective/icalendar/pull/1571"
        },
        {
          "name": "https://github.com/collective/icalendar/commit/157f85137c65565a308bbcf4fdcc7d8ebce01267",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/collective/icalendar/commit/157f85137c65565a308bbcf4fdcc7d8ebce01267"
        },
        {
          "name": "https://github.com/collective/icalendar/commit/cddd37226adbc52cca52a399f61d38a378221219",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/collective/icalendar/commit/cddd37226adbc52cca52a399f61d38a378221219"
        },
        {
          "name": "https://github.com/collective/icalendar/releases/tag/v7.2.2",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/collective/icalendar/releases/tag/v7.2.2"
        }
      ],
      "source": {
        "advisory": "GHSA-qjcq-q7h7-r74v",
        "discovery": "UNKNOWN"
      },
      "title": "icalendar: Denial of service via unbounded VALARM REPEAT expansion"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-77399",
    "datePublished": "2026-09-22T18:58:56.647Z",
    "dateReserved": "2026-08-20T19:55:27.023Z",
    "dateUpdated": "2026-09-22T18:58:56.647Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}