VulnerabilityPublished 9 Oct 2026Updated 6 Nov 2026

CVE-2026-107889: Cross-site Scripting

Source GCVE Database

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Authoritative record:CVE-2026-107889· Medium 5.5

Not known to be exploited · CVSS 5.5 Medium : update Red Hat build of Keycloak 26.6.8 when convenient.

Data as of 6 Nov 2026, 13:50 UTC

CVSS 3.1 base score

5.5Medium

How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

One scorer or none

CVSS scores by source
CNA (redhat)	CVSS 3.1	5.5

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: High
User Interaction: None
Scope: Changed
Confidentiality: Low
Integrity: Low
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: High: The attacker is authorized with (i.e., requires) privileges that provide significant (e.g., administrative) control over the vulnerable component that could affect component-wide settings and files.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Changed: An exploited vulnerability can affect resources beyond the security scope managed by the security authority of the vulnerable component. In this case, the vulnerable component and the impacted component are different and managed by different security authorities.
Confidentiality: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to the impacted component.
Integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 9 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 6 Nov 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

ghsa-gv8g-wx99-6r59

What to do

Patches and advisories

access.redhat.com/errata/RHSA-2026:95761 (opens in a new tab)

Affected software

Product	Affected	Fixed in
Red Hat build of Keycloak 26.6.8keycloak-services	Affected–	Fixed in–
Red Hat build of Keycloak 26.6.8rhbk/keycloak-rhel9	Affected–	Fixed in–
Red Hat Single Sign-On 7keycloak-services	Affected–	Fixed in–

AI-suggested

A security update addressing this vulnerability is available in Red Hat build of Keycloak version 26.6.8. Users should apply this official fix promptly to remediate the issue. No additional mitigation steps are indicated by the vendor advisory.

Description

A stored cross-site scripting (XSS) vulnerability exists in the login theme rendering component of Keycloak. This flaw allows a realm administrator to bypass the security filter that sanitizes user input, enabling the injection of malicious scripts into display fields. When users visit the affected login page, these scripts may execute in their browsers, potentially exposing data or interfering with user sessions. The vulnerability has a CVSS score of 5.5, indicating medium severity. A security update fixing this issue is available in Red Hat build of Keycloak version 26.6.8.

Impact

Successful exploitation allows a realm administrator to inject and store malicious scripts that execute in the browsers of users visiting the login page. This can result in unauthorized JavaScript execution, potentially leading to data exposure or session interference. The vulnerability requires high privileges (realm administrator) and does not allow remote unauthenticated attackers to exploit it. The CVSS score of 5.5 reflects a medium impact on confidentiality and integrity, with no impact on availability.

Summary

CVE-2026-107889 describes a stored XSS vulnerability in Keycloak's login theme rendering component. The root cause is a bypass of the input sanitization filter, permitting a realm administrator to store malicious JavaScript in display fields. This script executes in the browsers of users accessing the login page, which may lead to data exposure or session interference. Red Hat's advisory confirms the issue and provides a fixed package in Keycloak version 26.6.8. No known exploits in the wild have been reported.

CWE-79Improper Neutralization of Input During Web Page Generation (Cross-site Scripting) (opens in a new tab)
Base weaknessLikelihood of exploit: HighCWE Top 25 (2025): #1OWASP Top 10 A05:2025: Injection (opens in a new tab)
The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.
Architecture and Design · Libraries or Frameworks
Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
Implementation · Architecture and Design
Understand the context in which your data will be used and the encoding that will be expected. This is especially important when transmitting data between different components, or when generating outputs that can contain multiple encodings at the same time, such as web pages or multi-part mail messages.
Architecture and Design · Implementation · Attack Surface Reduction
Understand all the potential areas where untrusted inputs can enter your software: parameters or arguments, cookies, anything read from the network, environment variables, reverse DNS lookups, query results, request headers, URL components, e-mail, files, filenames, databases, and any external systems that provide…
OWASP Cheat Sheets
Cross Site Scripting Prevention (opens in a new tab)
DOM based XSS Prevention (opens in a new tab)
Injection Prevention (opens in a new tab)
Abuse Case (opens in a new tab)
Deserialization (opens in a new tab)
OWASP ASVS 4.0.3
V5.3.3 (opens in a new tab)
V1.5.1 (opens in a new tab)
Attack patterns
XSS Using MIME Type Mismatch (opens in a new tab)
DOM-Based XSS (opens in a new tab)
Reflected XSS (opens in a new tab)
Stored XSS (opens in a new tab)
Cross-Site Scripting (XSS) (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Patches and advisories

Affected software

Description

AI analysisMachine-generated, updated 6 Nov 2026, 13:50 UTC

WeaknessesCWE-79

Technical details

References

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