CVE-2021-26929

Name: CVE-2021-26929
Creator: NVD / NIST
Published: 2021-02-14T04:15:12.777+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 6.1/10EPSS 4.94%

Last modified Jun 17, 2026

CVE-2021-26929 is a medium-severity vulnerability rated 6.1/10 on the CVSS scale. An XSS issue was discovered in Horde Groupware Webmail Edition through 5.2.22 (where the Horde_Text_Filter library before 2.3.7 is used). The attacker can send a plain text e-mail message, with JavaScript encoded as a link or email that is mishandled by preProcess in Text2html.php, because bespoke use of \x00\x00\x00 and \x01\x01\x01 interferes with XSS defenses.. EPSS estimates a 4.94% chance of exploitation in the next 30 days.

Description

An XSS issue was discovered in Horde Groupware Webmail Edition through 5.2.22 (where the Horde_Text_Filter library before 2.3.7 is used). The attacker can send a plain text e-mail message, with JavaScript encoded as a link or email that is mishandled by preProcess in Text2html.php, because bespoke use of \x00\x00\x00 and \x01\x01\x01 interferes with XSS defenses.

Metrics

CVSS 3.1

6.1/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

EPSS Probability

4.94%

91.1th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-79

Affected Software

Vendor	Product	Versions
Horde	Groupware	<= 5.2.22
Debian	Debian Linux	9.0

References

http://packetstormsecurity.com/files/162187/Webmail-Edition-5.2.22-XSS-Remote-Code-Execution.htmlExploit, Third Party Advisory, VDB Entry
http://packetstormsecurity.com/files/162194/Horde-Groupware-Webmail-5.2.22-Cross-Site-Scripting.htmlThird Party Advisory
https://github.com/horde/webmail/releasesThird Party Advisory
https://lists.debian.org/debian-lts-announce/2021/02/msg00028.htmlMailing List, Third Party Advisory
https://lists.horde.org/archives/announce/2021/001298.htmlMailing List, Vendor Advisory
https://www.alexbirnberg.com/horde-xss.htmlExploit, Third Party Advisory
https://www.horde.org/apps/webmailVendor Advisory
http://packetstormsecurity.com/files/162187/Webmail-Edition-5.2.22-XSS-Remote-Code-Execution.htmlExploit, Third Party Advisory, VDB Entry
http://packetstormsecurity.com/files/162194/Horde-Groupware-Webmail-5.2.22-Cross-Site-Scripting.htmlThird Party Advisory
https://github.com/horde/webmail/releasesThird Party Advisory
https://lists.debian.org/debian-lts-announce/2021/02/msg00028.htmlMailing List, Third Party Advisory
https://lists.horde.org/archives/announce/2021/001298.htmlMailing List, Vendor Advisory
https://www.alexbirnberg.com/horde-xss.htmlExploit, Third Party Advisory
https://www.horde.org/apps/webmailVendor Advisory

Timeline

Published: Feb 14, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-26929?

How severe is CVE-2021-26929?

CVE-2021-26929 has a CVSS score of 6.1/10 (MEDIUM severity). The EPSS model estimates a 4.94% probability of exploitation in the next 30 days.

How do I fix CVE-2021-26929?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-26929?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST