Vulnerability in icalendar (CVE-2026-55099)
Summary
Vulnerability in icalendar (CVE-2026-55099). Risk of unauthorized operations or information disclosure. Exploitable via Component.__eq__. Mitigation: upgrade to 7.1.3 or later.
Original description
The description as published by the source.
Summary
Component.__eq__ compares subcomponents in O(2^n) time relative to nesting depth. Because the parser accepts arbitrarily nested components, a sub-kilobyte .ics file is enough to make a single equality check run for minutes or hang indefinitely. Any application that compares parsed components (==, !=, in, set/dict membership, deduplication, test assertions) against attacker-supplied calendar data is exposed to denial of service.
Details
Component subclasses dict and stores children in a separate subcomponents list. __eq__ (src/icalendar/cal/component.py:642-665) checks set-equivalence of children with two membership loops:
def __eq__(self, other):
if len(self.subcomponents) != len(other.subcomponents):
return False
if not super().__eq__(other):
return False
for subcomponent in self.subcomponents:
if subcomponent not in other.subcomponents:
return False
for subcomponent in other.subcomponents:
if subcomponent not in self.subcomponents:
return False
return True
Each ... not in ... test invokes __eq__ on the children. For a nested chain, both loops descend the full subtree, so each level spawns two recursive comparisons: T(n) = 2·T(n-1) → O(2^n).
Parsing does not gate this. Component.from_ical builds the structure iteratively and imposes no depth limit, so BEGIN:VEVENT blocks can be nested to any depth (parsing the payload below is inst…
Source: GitHub Security Advisories (Global) NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-55099 has been found in icalendar.
Attackers can target a specific entry point like Component.__eq__ over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 7.5/10.
What to do: upgrade icalendar to 7.1.3 or later.
If unsure, ask your IT team or search "icalendar CVE-2026-55099" on the vendor's site.
CVE-2026-55099 (icalendar) — CWE-400 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: Component.__eq__ / Component / dict / subcomponents
Patched: 7.1.3 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-400) exists in icalendar. Attackers reach the vulnerable code path via Component.__eq__ without authentication.
Check the vendor advisory for the affected versions of icalendar. Attack surface: Component.__eq__ / Component / dict / subcomponents.
Severity: High (CVSS 7.5/10). Risk of unauthorized operations or information disclosure.
Update to 7.1.3.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'icalendar' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'icalendar' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
icalendarを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade icalendar to 7.1.3ステージング環境で 7.1.3 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。