CVE-2026-34478
Apache Log4j Core: Log injection in Rfc5424Layout due to silent configuration incompatibility
Description
Apache Log4j Core's Rfc5424Layout https://logging.apache.org/log4j/2.x/manual/layouts.html#RFC5424Layout , in versions 2.21.0 through 2.25.3, is vulnerable to log injection via CRLF sequences due to undocumented renames of security-relevant configuration attributes. Two distinct issues affect users of stream-based syslog services who configure Rfc5424Layout directly: * The newLineEscape attribute was silently renamed, causing newline escaping to stop working for users of TCP framing (RFC 6587), exposing them to CRLF injection in log output. * The useTlsMessageFormat attribute was silently renamed, causing users of TLS framing (RFC 5425) to be silently downgraded to unframed TCP (RFC 6587), without newline escaping. Users of the SyslogAppender are not affected, as its configuration attributes were not modified. Users are advised to upgrade to Apache Log4j Core 2.25.4, which corrects this issue.
INFO
Published Date :
April 10, 2026, 4:16 p.m.
Last Modified :
April 24, 2026, 6:10 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 3.1 | HIGH | [email protected] | ||||
| CVSS 4.0 | MEDIUM | f0158376-9dc2-43b6-827c-5f631a4d8d09 | ||||
| CVSS 4.0 | MEDIUM | [email protected] |
Solution
- Upgrade Apache Log4j Core to version 2.25.4.
- Ensure Rfc5424Layout configuration is reviewed.
- Verify newline escaping and TLS settings.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-34478.
| URL | Resource |
|---|---|
| https://github.com/apache/logging-log4j2/pull/4074 | Issue Tracking Patch |
| https://lists.apache.org/thread/3k1clr2l6vkdnl4cbhjrnt1nyjvb5gwt | Mailing List Vendor Advisory |
| https://logging.apache.org/cyclonedx/vdr.xml | Product |
| https://logging.apache.org/log4j/2.x/manual/layouts.html#RFC5424Layout | Technical Description |
| https://logging.apache.org/security.html#CVE-2026-34478 | Vendor Advisory |
| http://www.openwall.com/lists/oss-security/2026/04/10/7 | Mailing List Third Party Advisory |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-34478 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-34478
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-34478 vulnerability anywhere in the article.
-
Daily CyberSecurity
Log4j’s “Silent” Security Gap: New Advisories Warn of Data Loss and TLS Bypasses
The Apache Log4j 2 ecosystem is facing a fresh wave of security concerns as four new vulnerabilities have been disclosed, highlighting critical flaws in how the library handles data sanitization and i ... Read more
The following table lists the changes that have been made to the
CVE-2026-34478 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
Initial Analysis by [email protected]
Apr. 24, 2026
Action Type Old Value New Value Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N Added CPE Configuration OR *cpe:2.3:a:apache:log4j:3.0.0:beta1:*:*:*:*:*:* *cpe:2.3:a:apache:log4j:3.0.0:beta2:*:*:*:*:*:* *cpe:2.3:a:apache:log4j:3.0.0:beta3:*:*:*:*:*:* *cpe:2.3:a:apache:log4j:*:*:*:*:*:*:*:* versions from (including) 2.21.0 up to (excluding) 2.25.4 Added Reference Type Apache Software Foundation: https://github.com/apache/logging-log4j2/pull/4074 Types: Issue Tracking, Patch Added Reference Type Apache Software Foundation: https://lists.apache.org/thread/3k1clr2l6vkdnl4cbhjrnt1nyjvb5gwt Types: Mailing List, Vendor Advisory Added Reference Type Apache Software Foundation: https://logging.apache.org/cyclonedx/vdr.xml Types: Product Added Reference Type Apache Software Foundation: https://logging.apache.org/log4j/2.x/manual/layouts.html#RFC5424Layout Types: Technical Description Added Reference Type Apache Software Foundation: https://logging.apache.org/security.html#CVE-2026-34478 Types: Vendor Advisory Added Reference Type CVE: http://www.openwall.com/lists/oss-security/2026/04/10/7 Types: Mailing List, Third Party Advisory -
CVE Modified by af854a3a-2127-422b-91ae-364da2661108
Apr. 10, 2026
Action Type Old Value New Value Added Reference http://www.openwall.com/lists/oss-security/2026/04/10/7 -
New CVE Received by [email protected]
Apr. 10, 2026
Action Type Old Value New Value Added Description Apache Log4j Core's Rfc5424Layout https://logging.apache.org/log4j/2.x/manual/layouts.html#RFC5424Layout , in versions 2.21.0 through 2.25.3, is vulnerable to log injection via CRLF sequences due to undocumented renames of security-relevant configuration attributes. Two distinct issues affect users of stream-based syslog services who configure Rfc5424Layout directly: * The newLineEscape attribute was silently renamed, causing newline escaping to stop working for users of TCP framing (RFC 6587), exposing them to CRLF injection in log output. * The useTlsMessageFormat attribute was silently renamed, causing users of TLS framing (RFC 5425) to be silently downgraded to unframed TCP (RFC 6587), without newline escaping. Users of the SyslogAppender are not affected, as its configuration attributes were not modified. Users are advised to upgrade to Apache Log4j Core 2.25.4, which corrects this issue. Added CVSS V4.0 AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X Added CWE CWE-117 Added CWE CWE-684 Added Reference https://github.com/apache/logging-log4j2/pull/4074 Added Reference https://lists.apache.org/thread/3k1clr2l6vkdnl4cbhjrnt1nyjvb5gwt Added Reference https://logging.apache.org/cyclonedx/vdr.xml Added Reference https://logging.apache.org/log4j/2.x/manual/layouts.html#RFC5424Layout Added Reference https://logging.apache.org/security.html#CVE-2026-34478