CVE-2024-27443: Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting (XSS) Vulnerability

Patch now

MEDIUM 6.1EXPLOITEDUPGRADE

CVE-2024-27443 is a medium-severity flaw (CVSS 6.1) affecting collaboration, reported as exploited in the wild. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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

Why this priority

EPSS top 2%: very likely to be exploited
Exploited in the wild (CISA KEV)

A fixed release or distro patch exists.

Risk facts

CVSS score	6.1 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	24.6% (top 2%)
CISA exploited list	Yes, fix due 2025-06-09
Weakness	CWE-79
Published	2024-08-12
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: zimbra

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2024-08-12 15:15 UTCPublished CVE record published
2025-05-19Exploited Added to the CISA Known Exploited Vulnerabilities list
2025-06-09Deadline CISA due date for US federal agencies to patch
2026-06-17 07:19 UTCUpdated Record last modified

zimbra collaboration UPGRADE

Affected: >= 10.0.0 and < 10.0.7 · 9.0.0 · 9.0.0 p0 · 9.0.0 p1 · 9.0.0 p10 · 9.0.0 p11 · 9.0.0 p12 · 9.0.0 p13

Fixed in: 10.0.7

Safe to downgrade to: a release before 9.0.0

1. Check installed version

apt-cache policy collaboration || rpm -q collaboration || collaboration --version

2. UPGRADE to 10.0.7 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade collaboration

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade collaboration

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 9.0.0 (Debian / Ubuntu)

apt-cache madison collaboration sudo apt install collaboration=<VERSION_BEFORE_9.0.0> sudo apt-mark hold collaboration

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list collaboration sudo dnf downgrade collaboration-<VERSION_BEFORE_9.0.0> sudo dnf versionlock add collaboration

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Exact fixes by distribution

Fedora ELN · gram_grep · FIXED · 0.10.4-1.eln159 · FEDORA-2026-0808475f2a · source

sudo dnf upgrade --advisory=FEDORA-2026-0808475f2a

Fedora 46 · wesnoth · FIXED · 1.19.29-1.fc46 · FEDORA-2026-58f458e24e · source

sudo dnf upgrade --advisory=FEDORA-2026-58f458e24e

Public exploits and detection

Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.

Nuclei scan template: Zimbra Collaboration - Cross-Site Scripting (XSS)

Verify at the official source NVD · CVE Program · CISA KEV catalog · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2024-27443?

collaboration: upgrade to 10.0.7. Exact commands for each OS are on this page.

Is CVE-2024-27443 being exploited?

Yes. CVE-2024-27443 is on the CISA Known Exploited Vulnerabilities list, so treat it as patch-now.

What does CVE-2024-27443 affect?

CVE-2024-27443 affects collaboration. Severity is medium (CVSS 6.1). 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 ha

How urgent is CVE-2024-27443?

Priority 71/100. EPSS top 2%: very likely to be exploited; Exploited in the wild (CISA KEV)

Software pages

Zimbra vulnerabilities

Related CVEs

CVE-2025-67809 MEDIUM 4.7 UPGRADE An issue was discovered in Zimbra Collaboration (ZCS) 10.0 and 10.1
CVE-2025-27914 MEDIUM 5.4 UPGRADE An issue was discovered in Zimbra Collaboration (ZCS) 9.0 and 10.0 and 10.1
CVE-2024-45515 MEDIUM 6.1 UPGRADE An issue was discovered in Zimbra Collaboration (ZCS) through 10.1
CVE-2024-33536 MEDIUM 5.4 UPGRADE An issue was discovered in Zimbra Collaboration (ZCS) 9.0 and 10.0
CVE-2024-33535 HIGH 7.5 UPGRADE An issue was discovered in Zimbra Collaboration (ZCS) 9.0 and 10.0

References

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