CVE-2021-28994: kopano-ical (formerly zarafa-ical) in Kopano Groupware Core through 8.7.16, 9.x through 9.1.0, 10.x through 10

This week

HIGH 7.5REMOTEUPGRADEUPGRADE

CVE-2021-28994 is a high-severity flaw (CVSS 7.5) affecting groupware core, zarafa. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

kopano-ical (formerly zarafa-ical) in Kopano Groupware Core through 8.7.16, 9.x through 9.1.0, 10.x through 10.0.7, and 11.x through 11.0.1 and Zarafa 6.30.x through 7.2.x allows memory exhaustion via long HTTP headers.

Why this priority

High severity
Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	2.0% (top 19%)
CISA exploited list	No
Weakness	CWE-770
Published	2021-03-31
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: kopano · zarafa

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

Am I affected?

Timeline

2021-03-31 23:15 UTCPublished CVE record published
2026-06-17 03:47 UTCUpdated Record last modified

kopano groupware core UPGRADE

Affected: <= 8.7.16 · >= 9.0.0 and <= 9.1.0 · >= 10.0.0 and <= 10.0.7 · >= 11.0.0 and <= 11.0.1

Fixed in: newer than 11.0.1

Safe to downgrade to: a release before 9.0.0

1. Check installed version

apt-cache policy groupware-core || rpm -q groupware-core || groupware-core --version

2. UPGRADE to newer than 11.0.1 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade groupware-core

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade groupware-core

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 groupware-core sudo apt install groupware-core=<VERSION_BEFORE_9.0.0> sudo apt-mark hold groupware-core

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

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

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.

zarafa zarafa UPGRADE

Affected: >= 6.30.0 and <= 7.2.6

Fixed in: newer than 7.2.6

Safe to downgrade to: a release before 6.30.0

1. Check installed version

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

2. UPGRADE to newer than 7.2.6 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade zarafa

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 6.30.0 (Debian / Ubuntu)

apt-cache madison zarafa sudo apt install zarafa=<VERSION_BEFORE_6.30.0> sudo apt-mark hold zarafa

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

dnf --showduplicates list zarafa sudo dnf downgrade zarafa-<VERSION_BEFORE_6.30.0> sudo dnf versionlock add zarafa

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.

Verify at the official source NVD · CVE Program · 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-2021-28994?

groupware core: upgrade to newer than 11.0.1; zarafa: upgrade to newer than 7.2.6. Exact commands for each OS are on this page.

Is CVE-2021-28994 being exploited?

CVE-2021-28994 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2021-28994 affect?

CVE-2021-28994 affects groupware core, zarafa. Severity is high (CVSS 7.5). kopano-ical (formerly zarafa-ical) in Kopano Groupware Core through 8.7.16, 9.x through 9.1.0, 10.x through 10.0.7, and 11.x through 11.0.1 and Zarafa 6.30.x through 7.2.x allows memory exhaustion via long HTTP headers.

How urgent is CVE-2021-28994?

Priority 57/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action

Related CVEs

CVE-2022-26562 CRITICAL 9.8 DOWNGRADE An issue in provider/libserver/ECKrbAuth.cpp of Kopano Core <= v11.0.2.51 contains an issue which allows attac

References

← Back to latest CVEs