Skip to content

[GHSA-3pxv-7cmr-fjr4] Apache Log4j Core's XmlLayout fails to sanitize characters #7361

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
ppkarwasz wants to merge 1 commit into
base: ppkarwasz/advisory-improvement-7361
Choose a base branch
from
+3 −3
Open

[GHSA-3pxv-7cmr-fjr4] Apache Log4j Core's XmlLayout fails to sanitize characters #7361

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
6 changes: 3 additions & 3 deletions advisories/github-reviewed/2026/04/GHSA-3pxv-7cmr-fjr4/GHSA-3pxv-7cmr-fjr4.json
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -6,8 +6,8 @@
"aliases": [
"CVE-2026-34480"
],
"summary": "Apache Log4j Core's XmlLayout fails to sanitize characters",
"details": "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.\n\nThe impact depends on the StAX implementation in use:\n\n * 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.\n * 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.\n\n\nUsers are advised to upgrade to Apache Log4j Core 2.25.4, which corrects this issue by sanitizing forbidden characters before XML output.",
"summary": "Apache Log4j Core: Silent log event loss in XmlLayout due to unescaped XML 1.0 forbidden characters",
Copy link

Copilot AI Apr 11, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

The summary says "unescaped XML 1.0 forbidden characters", but XML 1.0 forbidden characters generally can’t be made valid via escaping—Log4j needs to sanitize/remove/replace them. Consider rewording to "unsanitized"/"unsanitized forbidden characters" to avoid implying escaping is a viable fix.

Suggested change
"summary": "Apache Log4j Core: Silent log event loss in XmlLayout due to unescaped XML 1.0 forbidden characters",
"summary": "Apache Log4j Core: Silent log event loss in XmlLayout due to unsanitized XML 1.0 forbidden characters",

Copilot uses AI. Check for mistakes.
Copy link
Copy Markdown
Author

@ppkarwasz ppkarwasz Apr 11, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

This is the original summary we submitted, but the suggestion makes sense.

"details": "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.\n\nThe impact depends on the StAX implementation in use:\n\n * **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.\n * **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.\n\nUsers are advised to upgrade to Apache Log4j Core 2.25.4, which corrects this issue by sanitizing forbidden characters before XML output.",
Copy link

Copilot AI Apr 11, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Minor grammar: add punctuation after the XML 1.0 specification link (e.g., ") , producing…" or rephrase) so the opening sentence reads cleanly.

Suggested change
"details": "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.\n\nThe impact depends on the StAX implementation in use:\n\n * **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.\n * **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.\n\nUsers are advised to upgrade to Apache Log4j Core 2.25.4, which corrects this issue by sanitizing forbidden characters before XML output.",
"details": "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.\n\nThe impact depends on the StAX implementation in use:\n\n * **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.\n * **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.\n\nUsers are advised to upgrade to Apache Log4j Core 2.25.4, which corrects this issue by sanitizing forbidden characters before XML output.",

Copilot uses AI. Check for mistakes.
Copy link
Copy Markdown
Author

@ppkarwasz ppkarwasz Apr 11, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Makes sense

"severity": [
{
"type": "CVSS_V4",
Expand Down Expand Up @@ -47,7 +47,7 @@
"introduced": "3.0.0-alpha1"
},
{
"fixed": "3.0.0-beta3"
"last_affected": "3.0.0-beta3"
}
]
}
Expand Down
Loading