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CVE-2026-34478

Apache Log4j Core: Log injection in Rfc5424Layout due to silent configuration incompatibility

6.9 MediumFix available

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.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
None
Integrity
None
Availability
None

Exploit likelihood

0.97%Up 0.8 points since Apr 11, 2026
90%50%10%1%

What each source reports

CVE List Score used 6.9

Apache Log4j Core: Log injection in Rfc5424Layout due to silent configuration incompatibility

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.

Record
CVE-2026-34478
CVSS 4.0
6.9 MediumCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N
Weakness
CWE-684, CWE-117
Updated
2026-11-02
EUVDEUVD-2026-21408 6.9

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.

Record
EUVD-2026-21408
CVSS 4.0
6.9 MediumCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N
Updated
2026-11-02
GitHub AdvisoriesGHSA-445c-vh5m-36rj 6.9

Apache Log4j Core: log injection in `Rfc5424Layout` due to silent configuration incompatibility

Apache Log4j Core's 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.

Record
GHSA-445c-vh5m-36rj
CVSS 4.0
6.9 MediumCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N
Weakness
CWE-117, CWE-684
Updated
2026-11-02
NVD 6.9

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.

Record
CVE-2026-34478
CVSS 4.0
6.9 MediumCVSS:4.0/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
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Weakness
CWE-117, CWE-684
Updated
2026-11-02
OSV 6.9

Apache Log4j Core: Log injection in Rfc5424Layout due to silent configuration incompatibility

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.

Record
CVE-2026-34478
CVSS 4.0
6.9 MediumCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N
Weakness
CWE-117, CWE-684
Updated
2026-11-02
OSVGHSA-445c-vh5m-36rj 6.9

Apache Log4j Core: log injection in `Rfc5424Layout` due to silent configuration incompatibility

Apache Log4j Core's 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.

Record
GHSA-445c-vh5m-36rj
CVSS 4.0
6.9 MediumCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N
Weakness
CWE-117, CWE-684
Updated
2026-11-02
Show 7 moreShow less
OSVRHLW-2026-64cfac683d7a9af7 6.3

Lightwell Security Advisory: log4j-1.2-api 2.24.3.rhlw-00004

Red Hat Lightwell has released org.apache.logging.log4j:log4j-1.2-api 2.24.3.rhlw-00004 with backported fixes for CVE-2025-68161, CVE-2026-34477, CVE-2026-34478, and CVE-2026-34480.

CVE-2025-68161: Apache Log4j Core: Missing TLS hostname verification in Socket appender

CVE-2026-34477: Apache Log4j Core: verifyHostName attribute silently ignored in TLS configuration, allowing hostname verification bypass

CVE-2026-34478: Apache Log4j Core: Log injection in Rfc5424Layout due to silent configuration incompatibility

CVE-2026-34480: Apache Log4j Core: Silent log event loss in XmlLayout due to unescaped XML 1.0 forbidden characters

This patched artifact is a drop-in replacement for org.apache.logging.log4j:log4j-1.2-api 2.24.3 from Maven Central.

Record
RHLW-2026-64cfac683d7a9af7
CVSS 4.0
6.3 MediumCVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:L/SA:N
Updated
2026-11-02
OSVRHLW-2026-97a6348484d7bbf1 6.3

Lightwell Security Advisory: log4j-core 2.24.3.rhlw-00004

Red Hat Lightwell has released org.apache.logging.log4j:log4j-core 2.24.3.rhlw-00004 with backported fixes for CVE-2025-68161, CVE-2026-34477, CVE-2026-34478, and CVE-2026-34480.

CVE-2025-68161: Apache Log4j Core: Missing TLS hostname verification in Socket appender

CVE-2026-34477: Apache Log4j Core: verifyHostName attribute silently ignored in TLS configuration, allowing hostname verification bypass

CVE-2026-34478: Apache Log4j Core: Log injection in Rfc5424Layout due to silent configuration incompatibility

CVE-2026-34480: Apache Log4j Core: Silent log event loss in XmlLayout due to unescaped XML 1.0 forbidden characters

This patched artifact is a drop-in replacement for org.apache.logging.log4j:log4j-core 2.24.3 from Maven Central.

Record
RHLW-2026-97a6348484d7bbf1
CVSS 4.0
6.3 MediumCVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:L/SA:N
CVSS 3.1
5.9 MediumCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N
Updated
2026-11-02
OSVROOT-APP-MAVEN-CVE-2026-34478 7.5

CVE-2026-34478 in org.apache.logging.log4j:log4j-core - Patched by Root

Root has patched CVE-2026-34478 in the org.apache.logging.log4j:log4j-core package for Root:Maven. Multiple fixed versions available.

Record
ROOT-APP-MAVEN-CVE-2026-34478
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Updated
2026-11-02
OSVUBUNTU-CVE-2026-34478 6.9

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.

Record
UBUNTU-CVE-2026-34478
CVSS 4.0
6.9 MediumCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Updated
2026-11-06
OSVCLSA-2026-1787726168 No score

TuxCare security update for org.apache.logging.log4j (4 CVEs)

TuxCare rebuilt 3 org.apache.logging.log4j packages to address 4 CVEs. Fixed in 2.24.3-tuxcare.2.

Record
CLSA-2026-1787726168
Updated
2026-11-02
OSVCLSA-2026-1790709023 No score

TuxCare security update for org.apache.logging.log4j (3 CVEs)

TuxCare rebuilt 3 org.apache.logging.log4j packages to address 3 CVEs. Fixed in 2.24.1-tuxcare.1.

Record
CLSA-2026-1790709023
Updated
2026-11-02
OSVCLSA-2026-1793354113 No score

TuxCare security update for org.apache.logging.log4j (5 CVEs)

TuxCare rebuilt 3 org.apache.logging.log4j packages to address 5 CVEs. Fixed in 2.25.2-tuxcare.1.

Record
CLSA-2026-1793354113
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
org.apache.logging.log4j:log4j-core
Maven
 2.21.0 up to 2.25.4
2.25.4
org.apache.logging.log4j:log4j-core
Maven
 3.0.0-beta1 to 3.0.0-beta3 None known
org.apache.logging.log4j:log4j-1.2-api
TuxCare:Maven
From an advisory covering 4 CVEs
 2.24.3 up to 2.24.3-tuxcare.2, plus listed versions
2.24.3-tuxcare.1
2.24.3-tuxcare.2
org.apache.logging.log4j:log4j-api
TuxCare:Maven
From an advisory covering 4 CVEs
 2.24.3 up to 2.24.3-tuxcare.2, plus listed versions
2.24.3-tuxcare.1
2.24.3-tuxcare.2
org.apache.logging.log4j:log4j-core
TuxCare:Maven
From an advisory covering 4 CVEs
 2.24.3 up to 2.24.3-tuxcare.2, plus listed versions
2.24.3-tuxcare.1
2.24.3-tuxcare.2
org.apache.logging.log4j:log4j-1.2-api
TuxCare:Maven
From an advisory covering 3 CVEs
 2.24.1 up to 2.24.1-tuxcare.1
2.24.1-tuxcare.1
org.apache.logging.log4j:log4j-core
TuxCare:Maven
From an advisory covering 3 CVEs
 2.24.1 up to 2.24.1-tuxcare.1
2.24.1-tuxcare.1
org.apache.logging.log4j:log4j-layout-template-json
TuxCare:Maven
From an advisory covering 3 CVEs
 2.24.1 up to 2.24.1-tuxcare.1
2.24.1-tuxcare.1
org.apache.logging.log4j:log4j-1.2-api
TuxCare:Maven
From an advisory covering 5 CVEs
 2.25.2 up to 2.25.2-tuxcare.1
2.25.2-tuxcare.1
org.apache.logging.log4j:log4j-core
TuxCare:Maven
From an advisory covering 5 CVEs
 2.25.2 up to 2.25.2-tuxcare.1
2.25.2-tuxcare.1
Show 19 moreShow less
Affected packages
PackageAffectedFixed
org.apache.logging.log4j:log4j-layout-template-json
TuxCare:Maven
From an advisory covering 5 CVEs
 2.25.2 up to 2.25.2-tuxcare.1
2.25.2-tuxcare.1
org.apache.logging.log4j:log4j-core
Maven
 2.21.0 up to 2.25.4, plus listed versions
2.21.12.22.02.22.12.23.02.23.1
Show 8 moreShow less
2.24.02.24.12.24.22.24.32.25.02.25.12.25.22.25.3
2.25.4
org.apache.logging.log4j:log4j-core
Maven
 3.0.0-beta1 to 3.0.0-beta3, plus listed versions
3.0.0-beta2
 None known
org.apache.logging.log4j:log4j-1.2-api
Red Hat Lightwell:Maven
From an advisory covering 4 CVEs
 before 2.24.3.rhlw-00004, plus listed versions
2.02.0-beta52.0-beta62.0-beta72.0-beta8
Show 45 moreShow less
2.0-beta92.0-rc12.0-rc22.0.12.0.22.12.10.02.11.02.11.12.11.22.12.02.12.12.12.22.12.32.12.42.13.02.13.12.13.22.13.32.14.02.14.12.15.02.16.02.17.02.17.12.17.22.18.02.19.02.22.20.02.21.02.21.12.22.02.22.12.23.02.23.12.24.02.24.12.24.22.24.32.32.3.12.3.22.42.4.1
2.24.3.rhlw-00004
org.apache.logging.log4j:log4j-core
Red Hat Lightwell:Maven
From an advisory covering 4 CVEs
 before 2.24.3.rhlw-00004, plus listed versions
2.02.0-alpha12.0-alpha22.0-beta12.0-beta2
Show 45 moreShow less
2.0-beta32.0-beta42.0-beta52.0-beta62.0-beta72.0-beta82.0-beta92.0-rc12.0-rc22.0.12.0.22.12.10.02.11.02.11.12.11.22.12.02.12.12.12.22.12.32.12.42.13.02.13.12.13.22.13.32.14.02.14.12.15.02.16.02.17.02.17.12.17.22.18.02.19.02.22.20.02.21.02.21.12.22.02.22.12.23.02.23.12.24.02.24.12.24.2
2.24.3.rhlw-00004
org.apache.logging.log4j:log4j-core
Root:Maven
 before 2.25.0-aikido.11
2.25.0-aikido.112.24.0-aikido.22.23.1-aikido.22.25.0-aikido.122.21.1-aikido.52.23.1-aikido.32.25.3-aikido.12.24.3-aikido.12.25.3-aikido.2
io.root.org.apache.logging.log4j:log4j-core
Root:Maven
 before 2.25.0-root.io.2
2.25.0-root.io.22.25.0-root.io.102.23.1-root.io.12.21.1-root.io.12.24.0-root.io.12.25.0-root.io.112.24.0-root.io.22.23.1-root.io.22.21.1-root.io.42.25.0-root.io.122.21.1-root.io.52.23.1-root.io.32.25.3-root.io.12.24.3-root.io.12.25.3-root.io.2
apache-log4j1.2
Ubuntu:Pro:14.04:LTS
 All versions, plus listed versions
1.2.17-3ubuntu11.2.17-4ubuntu11.2.17-4ubuntu21.2.17-4ubuntu31.2.17-4ubuntu3+esm11.2.17-4ubuntu3+esm2
 None known
apache-log4j2
Ubuntu:Pro:16.04:LTS
 All versions, plus listed versions
2.2-12.4-12.4-22.4-2ubuntu0.1~esm1
 None known
apache-log4j1.2
Ubuntu:Pro:16.04:LTS
 All versions, plus listed versions
1.2.17-6ubuntu11.2.17-7ubuntu11.2.17-7ubuntu1+esm11.2.17-7ubuntu1+esm2
 None known
apache-log4j1.2
Ubuntu:18.04:LTS
 All versions, plus listed versions
1.2.17-7ubuntu21.2.17-81.2.17-8+deb10u1build0.18.04.11.2.17-8+deb10u1ubuntu0.11.2.17-8+deb10u1ubuntu0.2
 None known
apache-log4j1.2
Ubuntu:20.04:LTS
 All versions, plus listed versions
1.2.17-81.2.17-91.2.17-9ubuntu0.11.2.17-9ubuntu0.2
 None known
apache-log4j1.2
Ubuntu:22.04:LTS
 All versions, plus listed versions
1.2.17-101.2.17-11
 None known
apache-log4j1.2
Ubuntu:24.04:LTS
 All versions, plus listed versions
1.2.17-11
 None known
apache-log4j1.2
Ubuntu:25.10
 All versions, plus listed versions
1.2.17-11
 None known
apache-log4j2
Ubuntu:25.10
 All versions, plus listed versions
2.19.0-2
 None known
apache-log4j1.2
Ubuntu:26.10
 All versions, plus listed versions
1.2.17-11build1
 None known
apache-log4j2
Ubuntu:26.10
 All versions, plus listed versions
2.19.0-2build1
 None known
apache-log4j1.2
Ubuntu:26.04:LTS
 All versions, plus listed versions
1.2.17-111.2.17-11build1
 None known

History

History
RecordedChangedSources
affectedOSV
affected, facts
first indexedCVE List, EUVD, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-34478 is a medium vulnerability (CVSS 6.9) in Apache Log4j, published April 10, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.97%, the 62nd percentile. Fixed in org.apache.logging.log4j:log4j-core 2.25.4.

References

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Left out here: 26 versions. The JSON record has them.

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