Reflected XSS via client window id in URL client window mode
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
- Exploited
- No known exploitation
- Fix
- Fixed in 4.0.29, 4.1.20, 5.0.0-M12
- Who is exposed
- Not reported
Do first: Upgrade to a fixed version: 4.0.29, 4.1.20, 5.0.0-M12.
- Exploitation0/40No signal
- Exposure7/25Reachable over the network without a login · Data gap: No advisory context yet
- Reach?/20Reach: unknown (data gap). No tracked technology or package matched
- Severity6.1/10CVSS 6.1
- No patch0/5No signal
What would change the score
- Would score about 68 if added to CISA KEV
- Would score about 63 if CISA's SSVC rates exploitation active
- Would score about 28 if advisories confirm default setups are exposed
CVE-2026-120421 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 6.1 (medium) and affects Eclipse Mojarra; fixed in 4.0.29, 4.1.20 and 5.0.0-M12.
- Last modified
- Where the record stands: published, rejected by its publisher, or superseded by another id.What do these mean? →
- Published
- Whether CISA lists it in its Known Exploited Vulnerabilities catalog: proof that attackers are using it.What do these mean? →
- Not listed in CISA KEV
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 13/100 · provisional
- Fix
- Fixed in 4.0.29, 4.1.20, 5.0.0-M12
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
- Exploitation: none
- Automatable: no
- Technical impact: partial
Summary
Eclipse Mojarra, the Jakarta Faces implementation, is affected when URL client window mode is enabled, and an attacker can remotely inject script into a page without logging in, though a user must take an action such as visiting a crafted link. Because the client window id is not URL-encoded before it is placed in a JavaScript string on the page, the injected script runs in the victim's browser, and when the nonce-based CSP option is turned on, the script can also bypass the Content Security Policy.
Read the original description
In Eclipse Mojarra versions 2.2.0 through 4.0.28, 4.1.0 through 4.1.19, and 5.0.0-M1 through 5.0.0-M11, when URL client window mode is enabled (`jakarta.faces.CLIENT_WINDOW_MODE=url`), the client window id from the `jfwid` or `jakarta.faces.ClientWindow` request parameter is appended to generated URLs without URL-encoding. `h:button` renders such a URL into a JavaScript string literal, which allows reflected cross-site scripting. With `com.sun.faces.enableCspNonce=true`, the injected script runs on page load inside the nonce script element, bypassing the Content Security Policy.
What to do
Upgrade to a fixed version: 4.0.29, 4.1.20, 5.0.0-M12.
Timeline
- CVE published
- First seen by cve.now
- CISA SSVC assessment
Exploitation: none · Automatable: no · Technical impact: partial
- Record last updated
Affected versions
- Eclipse Foundation Eclipse Mojarra
From 2.2.0 · fixed in 4.0.29; From 4.1.0 · fixed in 4.1.20; From 5.0.0-M1 · fixed in 5.0.0-M12
Evidence 2
- Link
- Link
Corrections
None so far.
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Questions about CVE-2026-120421
Is CVE-2026-120421 being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data
Which versions are affected by CVE-2026-120421?
Eclipse Mojarra: from 2.2.0 before 4.0.29; from 4.1.0 before 4.1.20; from 5.0.0-M1 before 5.0.0-M12.Source: cve.now feed data
How do I fix CVE-2026-120421?
Upgrade to a fixed version: 4.0.29, 4.1.20, 5.0.0-M12.Source: cve.now feed data