How severe is CVE-2021-26929?

CVE-2021-26929 has a CVSS 3.x base score of 6.1, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is low, integrity low, and availability none.

Is CVE-2021-26929 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 5% (91st percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-26929?

CVE-2021-26929 primarily affects Horde Groupware. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-26929?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2021-26929 published?

CVE-2021-26929 was published on 2021-02-14 and last updated on 2026-06-17.

CVE-2021-26929

CVE-2021-26929 is a medium-severity vulnerability in Horde Groupware with a CVSS 3.x base score of 6.1. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-79.

Key facts

Severity: Medium (CVSS 3.x base score 6.1)
CVSS v2: 4.3
EPSS exploit prediction: 5% (91st percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-79
Affected product: Horde Groupware
Published: 2021-02-14
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2021-26929?: 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.
How severe is CVE-2021-26929?: CVE-2021-26929 has a CVSS 3.x base score of 6.1, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is low, integrity low, and availability none.
Is CVE-2021-26929 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 5% (91st percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-26929?: CVE-2021-26929 primarily affects Horde Groupware. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-26929?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-26929 published?: CVE-2021-26929 was published on 2021-02-14 and last updated on 2026-06-17.

References

Affected products (2)

cpe:2.3:a:horde:groupware:*:*:*:*:webmail:*:*:*
cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:*

More vulnerabilities in Horde Groupware

CVE-2008-7219 — Critical (CVSS 10.0): Horde Kronolith H3 2.1 before 2.1.7 and 2.2 before 2.2-RC2; Nag H3 2.1 before 2.1.4 and 2.2 before 2.2-RC2; Mnemo H3…
CVE-2008-7218 — Critical (CVSS 10.0): Unspecified vulnerability in the Horde API in Horde 3.1 before 3.1.6 and 3.2 before 3.2 before 3.2-RC2; Turba H3 2.1…
CVE-2020-8518 — Critical (CVSS 9.8): Horde Groupware Webmail Edition 5.2.22 allows injection of arbitrary PHP code via CSV data, leading to remote code…
CVE-2013-6364 — High (CVSS 8.8): Horde Groupware Webmail Edition has CSRF and XSS when saving search as a virtual address book
CVE-2019-12095 — High (CVSS 8.8): Horde Trean, as used in Horde Groupware Webmail Edition through 5.2.22 and other products, allows CSRF, as demonstrated…
CVE-2019-9858 — High (CVSS 8.8): Remote code execution was discovered in Horde Groupware Webmail 5.2.22 and 5.2.17. Horde/Form/Type.php contains a…

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