CVE-2020-8866: This vulnerability allows remote attackers to create arbitrary files on affected installations of Horde Groupw

Q: How do I fix CVE-2020-8866?

groupware: downgrade or apply the listed mitigation; horde form: upgrade to 2.0.20; debian linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Q: Is CVE-2020-8866 being exploited?

CVE-2020-8866 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2020-8866 affect?

CVE-2020-8866 affects groupware, horde form, debian linux. Severity is medium (CVSS 6.5). This vulnerability allows remote attackers to create arbitrary files on affected installations of Horde Groupware Webmail Edition 5.2.22. Authentication is required to exploit this vulnerability. The specific flaw exists within add.php. The

Q: How urgent is CVE-2020-8866?

Priority 57/100. EPSS top 5%: very likely to be exploited; Public exploit reference; On your watchlist

This week

MEDIUM 6.5WATCHLISTDOWNGRADEUPGRADEMITIGATE

CVE-2020-8866 is a medium-severity flaw (CVSS 6.5) affecting groupware, horde form, debian linux. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

This vulnerability allows remote attackers to create arbitrary files on affected installations of Horde Groupware Webmail Edition 5.2.22. Authentication is required to exploit this vulnerability. The specific flaw exists within add.php. The issue results from the lack of proper validation of user-supplied data, which can allow the upload of arbitrary files. An attacker can leverage this in conjunction with other vulnerabilities to execute code in

Why this priority

EPSS top 5%: very likely to be exploited
Public exploit reference
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	6.5 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	9.6% (top 5%)
CISA exploited list	No
Weakness	CWE-434
Published	2020-03-23
Last modified	2026-06-17

Publisher (CNA): Zero Day Initiative · Vendor: debian · horde

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

Am I affected?

Timeline

2020-03-23 21:15 UTCPublished CVE record published
2026-06-17 03:27 UTCUpdated Record last modified

horde groupware DOWNGRADE

Affected: 5.2.22

Fixed in: no fixed release known

Safe to downgrade to: a release before 5.2.22

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 5.2.22 (Debian / Ubuntu)

apt-cache madison groupware sudo apt install groupware=<VERSION_BEFORE_5.2.22> sudo apt-mark hold groupware

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list groupware sudo dnf downgrade groupware-<VERSION_BEFORE_5.2.22> sudo dnf versionlock add groupware

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.

horde horde form UPGRADE

Affected: < 2.0.20

Fixed in: 2.0.20

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy horde-form || rpm -q horde-form || horde-form --version

2. UPGRADE to 2.0.20 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade horde-form

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade horde-form

Note

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

debian debian linux MITIGATE

Affected: 8.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 8.0

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

Public exploits and detection

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

Exploit-DB: Horde Groupware Webmail Edition 5.2.22 - PHAR Loading
Exploit-DB: Horde Groupware Webmail Edition 5.2.22 - PHP File Inclusion

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-2020-8866?

groupware: downgrade or apply the listed mitigation; horde form: upgrade to 2.0.20; debian linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2020-8866 being exploited?

CVE-2020-8866 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-2020-8866 affect?

CVE-2020-8866 affects groupware, horde form, debian linux. Severity is medium (CVSS 6.5). This vulnerability allows remote attackers to create arbitrary files on affected installations of Horde Groupware Webmail Edition 5.2.22. Authentication is required to exploit this vulnerability. The specific flaw exists within add.php. The

How urgent is CVE-2020-8866?

Priority 57/100. EPSS top 5%: very likely to be exploited; Public exploit reference; On your watchlist

Software pages

PHP vulnerabilities · Debian vulnerabilities

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References

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