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Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting (XSS) Vulnerability

Exploited · KEV 2025-05-19CVE-2024-27443CWE-79

Exploited since 2025-05-19. No WAF vendor names it yet. Our CRS test: not blocked.

Edge rules
0/8
Our test
Not blocked
CVSS
6.1
EPSS
24.6% Top 2%
Posts, 14d
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Published
2024-08-12
An issue was discovered in Zimbra Collaboration (ZCS) 9.0 and 10.0. A Cross-Site Scripting (XSS) vulnerability exists in the CalendarInvite feature of the Zimbra webmail classic user interface, because of improper input validation in the… More

An issue was discovered in Zimbra Collaboration (ZCS) 9.0 and 10.0. A Cross-Site Scripting (XSS) vulnerability exists in the CalendarInvite feature of the Zimbra webmail classic user interface, because of improper input validation in the handling of the calendar header. An attacker can exploit this via an email message containing a crafted calendar header with an embedded XSS payload. When a victim views this message in the Zimbra webmail classic interface, the payload is executed in the context of the victim's session, potentially leading to execution of arbitrary JavaScript code.

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Ask about CVE-2024-27443: who's covered, what to patch first, how vendors compare. I cite sources and won't help with attacks.

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Severity, decoded

CVSS 3.1
Medium · 6.1 / 10

Exploitable over the network, with no privileges and user interaction, leading to low impact on confidentiality and integrity, and the impact can reach components beyond the vulnerable one.

Over the internetNo login neededNeeds a user to actWorks reliablySpreads beyond the app
How the score is built8 metrics
  • Attack vectorAn attacker can reach it over the internet; no access to your network needed.
    Network
  • Attack complexityNo special conditions are needed; the attack works reliably.
    Low
  • Privileges requiredNo account or login is needed.
    None
  • User interactionA user has to do something first, such as open a file or click a link.
    Required
  • ScopeThe attack can spread beyond the vulnerable component to other parts of the system.
    Changed
  • Confidentiality impactAn attacker can read some data, but has no control over what they get.
    Low
  • Integrity impactAn attacker can change some data, but with limited control or limited effect.
    Low
  • Availability impactThe component keeps working normally.
    None
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
CISA's assessmentSSVC, from the CVE record
ExploitationActive

Attackers are exploiting this in the wild.

AutomatableNo

At least one step needs hands-on work, which slows mass attacks.

Technical impactTotal

A successful attack gives full control over the affected software or all of its data.

Public exploits

1 found
0 Metasploit0 Exploit-DB1 Scanner template0 GitHub PoCs

Links are to third-party code: never run it outside an isolated lab.

Timeline

  1. 2024-08-12
    CVE published
    CVE List
  2. 2025-05-19
    Added to CISA KEV
    Confirmed exploitation in the wild
  3. 2026-11-02
    Our test: OWASP Core Rule Set let it through
    paranoia level 1, anomaly threshold 5, default CRS settings
  4. 2026-11-02
    Our test: OWASP Core Rule Set let it through
    paranoia level 2, anomaly threshold 5, default CRS settings

Social

2026-10-21: 0 posts2026-10-22: 0 posts2026-10-23: 0 posts2026-10-24: 0 posts2026-10-25: 0 posts2026-10-26: 0 posts2026-10-27: 0 posts2026-10-28: 0 posts2026-10-29: 0 posts2026-10-30: 0 posts2026-10-31: 0 posts2026-11-01: 0 posts2026-11-02: 0 posts2026-11-03: 0 posts

No posts seen yet on X, Bluesky, Mastodon, Hacker News or GitHub.

Vendor statements

Quoted
CloudflareWAF Managed RulesBefore feed history

The CVE predates the oldest entry in this vendor's public feed, so a rule may exist that we cannot see.

AWSAWS WAF Managed RulesNo public claim

We found no public statement from this vendor naming this CVE. That is not proof of no protection: generic rules may still catch it. AWS often describes a vulnerability without naming its CVE (for example "Log4j"). We count only entries that name the CVE, so AWS coverage is understated.

Microsoft AzureFront Door and Application Gateway WAF (DRS)No public claim

We found no public statement from this vendor naming this CVE. That is not proof of no protection: generic rules may still catch it. The rule tables name CVEs but carry no dates, so Azure is left out of every time-to-rule figure.

Google CloudCloud Armor preconfigured WAF rulesNo public claim

We found no public statement from this vendor naming this CVE. That is not proof of no protection: generic rules may still catch it. Google names few CVEs: the release notes start in May 2024 and the rules reference lists CVEs without dates. Its cve-canary rules are opt-in.

FastlyNext-Gen WAF virtual patchesBefore feed history

The CVE predates the oldest entry in this vendor's public feed, so a rule may exist that we cannot see.

F5Attack signatures (Distributed Cloud WAF)No public claim

We found no public statement from this vendor naming this CVE. That is not proof of no protection: generic rules may still catch it. Each signature lists the CVEs it references, with its id and date. F5 does not state a default action; signatures enforce once staging ends in your policy.

AkamaiApp & API Protector (Adaptive Security Engine)No public source

This vendor publishes no machine-readable rule changelog we can check.

OWASP CRSCore Rule Set (open source, used inside many WAFs)No public claim

We found no public statement from this vendor naming this CVE. That is not proof of no protection: generic rules may still catch it. CRS rarely names CVEs: it relies on generic detections. Our own lab measures what it actually blocks.