CVE-2026-100263: In JetBrains YouTrack before 2026.2.18991 stored HTML injection via the User-Agent header was possible

Q: How do I fix CVE-2026-100263?

youtrack: upgrade to 2026.2.18991. Exact commands for each OS are on this page.

Q: Is CVE-2026-100263 being exploited?

CVE-2026-100263 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-2026-100263 affect?

CVE-2026-100263 affects youtrack. Severity is medium (CVSS 4.7). In JetBrains YouTrack before 2026.2.18991 stored HTML injection via the User-Agent header was possible

Q: How urgent is CVE-2026-100263?

Priority 19/100. No elevated risk signals yet.

Routine

MEDIUM 4.7UPGRADE

CVE-2026-100263 is a medium-severity flaw (CVSS 4.7) affecting youtrack. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

In JetBrains YouTrack before 2026.2.18991 stored HTML injection via the User-Agent header was possible

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	4.7 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	0.2% (top 91%)
CISA exploited list	No
Weakness	CWE-79
Published	2026-09-30
Last modified	2026-10-02

Publisher (CNA): JetBrains s.r.o. · Vendor: jetbrains

Last updated 2026-10-02 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-09-30 16:16 UTCPublished CVE record published
2026-10-02 20:23 UTCUpdated Record last modified

jetbrains youtrack UPGRADE

Affected: < 2026.2.18991

Fixed in: 2026.2.18991

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to 2026.2.18991 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade youtrack

Note

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

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-2026-100263?

youtrack: upgrade to 2026.2.18991. Exact commands for each OS are on this page.

Is CVE-2026-100263 being exploited?

CVE-2026-100263 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-2026-100263 affect?

CVE-2026-100263 affects youtrack. Severity is medium (CVSS 4.7). In JetBrains YouTrack before 2026.2.18991 stored HTML injection via the User-Agent header was possible

How urgent is CVE-2026-100263?

Priority 19/100. No elevated risk signals yet.

Related CVEs

CVE-2026-33392 HIGH 7.2 UPGRADE In JetBrains YouTrack before 2025.3.131383 high privileged user can achieve RCE via sandbox bypass
CVE-2026-57923 MEDIUM 5.3 UPGRADE In JetBrains YouTrack before 2026.2.16593 improper authorisation in the app configurations endpoint allowed mo
CVE-2026-57921 MEDIUM 4.3 UPGRADE In JetBrains YouTrack before 2026.2.16593 improper access control allowed reading users' private data via the
CVE-2026-57924 MEDIUM 4.3 UPGRADE In JetBrains YouTrack before 2026.2.16593 default role configuration exposed excessive user profile details
CVE-2026-57925 MEDIUM 4.3 UPGRADE In JetBrains YouTrack before 2026.2.16593 improper access control allowed reading saved queries and tags

References

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