Advisory details:
github_osv / GHSA-3pxv-7cmr-fjr4
| Advisory ID | github_osv/GHSA-3pxv-7cmr-fjr4 |
| Aliases |
CVE-2026-34480
|
| Summary | Apache Log4j Core: Silent log event loss in XmlLayout due to unescaped XML 1.0 forbidden characters 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 malformed XML. Conforming parsers must reject such documents with a fatal error, which may cause downstream log-processing systems to drop the affected records. * **Alternative StAX implementations** (e.g., [Woodstox](https://github.com/FasterXML/woodstox), a transitive dependency of the Jackson XML Dataformat module): An exception is thrown during the logging call, and the log event is never delivered to its intended appender, only to Log4j's internal status logger. Users are advised to upgrade to Apache Log4j Core 2.25.4, which corrects this issue by sanitizing forbidden characters before XML output. |
| Status | Published |
| Exploitability | 0.5 |
| Weighted Severity | 6.2 |
| Risk | 3.1 |
| Affected and Fixed Packages | Package Details |
| Introduced and Fixed Package Commit Patches | Package Commit Patches Details |
| System | Score | Found at |
|---|---|---|
| cvssv4 | 6.9 | https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/04/GHSA-3pxv-7cmr-fjr4/GHSA-3pxv-7cmr-fjr4.json |
| generic_textual | MODERATE |
| Reference id | Reference type | URL |
|---|---|---|
| https://github.com/apache/logging-log4j2 | ||
| https://logging.apache.org/cyclonedx/vdr.xml | ||
| http://www.openwall.com/lists/oss-security/2026/04/10/9 | ||
| 4077 | Other | https://github.com/apache/logging-log4j2/pull/4077 |
| 5x0hcnng0chhghp6jgjdp3qmbbhfjzhb | Advisory | https://lists.apache.org/thread/5x0hcnng0chhghp6jgjdp3qmbbhfjzhb |
| CVE-2026-34480 | https://nvd.nist.gov/vuln/detail/CVE-2026-34480 | |
| layouts.html#XmlLayout | Other | https://logging.apache.org/log4j/2.x/manual/layouts.html#XmlLayout |
| security.html#CVE-2026-34480 | Advisory | https://logging.apache.org/security.html#CVE-2026-34480 |
No EPSS data available for this advisory.
| Patch URL | |
|---|---|
| There are no known patches. | |
| Attack Vector (AV) | Attack Complexity (AC) | Attack Requirements (AT) | Privileges Required (PR) | User Interaction (UI) | Vulnerable System Impact Confidentiality (VC) | Vulnerable System Impact Integrity (VI) | Vulnerable System Impact Availability (VA) | Subsequent System Impact Confidentiality (SC) | Subsequent System Impact Integrity (SI) | Subsequent System Impact Availability (SA) |
|---|---|---|---|---|---|---|---|---|---|---|
network adjacent local physical |
low high |
none present |
none low high |
none passive active |
high low none |
high low none |
high low none |
high low none |
high low none |
high low none |
Vector: SSVCv2/E:N/A:Y/T:P/P:M/B:A/M:M/D:T/2026-04-10T17:43:51Z/
Decision: Track
Source URL: https://github.com/cisagov/vulnrichment/blob/develop/2026/34xxx/CVE-2026-34480.json
Source Advisory: vulnrichment/CVE-2026-34480
[{'Exploitation': 'none'},
{'Automatable': 'yes'},
{'Technical Impact': 'partial'},
{'Mission Prevalence': 'minimal'},
{'Public Well-being Impact': 'material'},
{'Mission & Well-being': 'medium'}]