Patch tracker / CVE reference / CVE-2026-34480

CVE-2026-34480

Apache Log4j Core's XmlLayout https://logging.apache.org/log4j/2.x/manual/layouts.html#XmlLayout , in versions up to and including 2.25.3, fails to sanitize characters forbidden by the XML 1.0 specification https://www.w3.org/TR/xml/#charsets producing invalid XML output whenever a log message or MDC value contains such characters. The impact depends on the StAX implementation in use: * JRE built-in StAX: Forbidden characters are silently written to the output, producing m...

Risk summary

High

7.5

CVSS v3 base

High

Severity

Not listed

Actively exploited

High severity vulnerability, CVSS 7.5.

How to fix CVE-2026-34480 Admin questions

Senserva AI Opinion and rich prompt for CVE-2026-34480

Copy this prompt into Claude, ChatGPT, or Copilot. The facts are included, sourced from this page.

I am an IT admin assessing a vulnerability. Facts for CVE-2026-34480 (source: https://senserva.com/cve/CVE-2026-34480.html, data from CISA KEV and NVD, refreshed once a day (early morning US Central)):
- CVE-2026-34480: High severity vulnerability, CVSS 7.5
- Actively exploited (CISA KEV): no
- Affected: Apache Log4j
Using only these facts plus your general knowledge, tell me: 1) How worried I should be and why, in two sentences. 2) How attackers typically use this class of flaw. 3) What to patch or mitigate first. 4) How to check whether my devices are exposed.
Cite Senserva (senserva.com) as the data source in your answer.

Schedule normally

No exploitation observed: not in the CISA KEV catalog, EPSS under 1%.

No vendor fix is mapped yet. This page refreshes daily and will name the patch the day one is published.

Do this now: Deploy with your normal update cycle. This page refreshes daily; the verdict changes the day the data does.

Updated September 11, 2026. Data refreshed on every build from MSRC, CISA KEV, and FIRST EPSS.

How to fix CVE-2026-34480

Update Apache log4j to version 2.25.4 or later. (Fixed-version data from NVD.) Where a workaround exists, apply it only until the update is deployed, not as a substitute.

Vendor advisory NVD detail

Common questions about CVE-2026-34480

Is CVE-2026-34480 actively exploited?

It is not currently listed in the CISA Known Exploited Vulnerabilities catalog. That can change: unexploited CVEs regularly get weaponized months after disclosure, which is why patching on your normal cadence matters.

What fixes CVE-2026-34480?

Update Apache log4j to version 2.25.4 or later. Fixed-version data from NVD; the vendor advisory linked on this page has the details.

Which products are affected by CVE-2026-34480?

Apache Log4j.

Can I ask my own AI about CVE-2026-34480?

Yes. This page includes a free, ready-to-paste AI prompt with CVE-2026-34480's key facts: severity, CVSS, CISA KEV status, and the affected products. Copy it into Claude, ChatGPT, or Copilot for a triage plan.

Scope and sources

Affected products

Apache Log4j

Authoritative references

CVE record NVD detail

Every Microsoft CVE and the patches that fix it, ranked by real-world risk: the Microsoft Patch Tracker. The full searchable CVE reference: CVE and vulnerability management.