CVE-2026-34478VulnerabilityPublished 10 Apr 2026Updated 6 Nov 2026

Apache log4j1.2: Apache Log4j Core's Rfc5424Layout

Affects apache-log4j1.2Source GCVE Database

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Authoritative record:CVE-2026-34478· Medium 6.9

Not known to be exploited · CVSS 6.9 Medium · fixed in 2.25.4 : update apache-log4j1.2 when convenient.

Data as of 6 Nov 2026, 15:38 UTC

CVSS 4.0 base score

6.9Medium

How severe the flaw is on the 0–10 CVSS scale.

Patch: Available – fixed in 2.25.4

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N

Attack Vector: Network
Attack Complexity: Low
Attack Requirements: None
Privileges Required: None
User Interaction: None
Vulnerable system confidentiality: None
Vulnerable system integrity: None
Vulnerable system availability: None
Subsequent system confidentiality: None
Subsequent system integrity: Low
Subsequent system availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, up to and including the entire Internet. Such a vulnerability is often termed “remotely exploitable” and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Attack Requirements: None: The successful attack does not depend on the deployment and execution conditions of the vulnerable system. The attacker can expect to be able to reach the vulnerability and execute the exploit under all or most instances of the vulnerability.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without interaction from any human user, other than the attacker.
Vulnerable system confidentiality: None: There is no loss of confidentiality within the Vulnerable System.
Vulnerable system integrity: None: There is no loss of integrity within the Vulnerable System.
Vulnerable system availability: None: There is no impact to availability within the Vulnerable System.
Subsequent system confidentiality: None: There is no loss of confidentiality within the Subsequent System or all confidentiality impact is constrained to the Vulnerable System.
Subsequent system integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact to the Subsequent System.
Subsequent system availability: None: There is no impact to availability within the Subsequent System or all availability impact is constrained to the Vulnerable System.

Definitions: FIRST CVSS v4.0 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 10 Apr 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 6 Nov 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Affected software

Product	Affected	Fixed in
Ubuntu 26.10apache-log4j1.2`pkg:deb/ubuntu/apache-log4j1.2?arch=source&distro=stonking`Other threats	Affected =1.2.17-11build1	Fixed in–
Ubuntu 26.10apache-log4j2`pkg:deb/ubuntu/apache-log4j2?arch=source&distro=stonking`Other threats	Affected =2.19.0-2build1	Fixed in–
Ubuntu 26.04 LTSapache-log4j1.2`pkg:deb/ubuntu/apache-log4j1.2?arch=source&distro=resolute`Other threats	Affected =1.2.17-11 =1.2.17-11build1	Fixed in–
Ubuntu 25.10apache-log4j1.2`pkg:deb/ubuntu/apache-log4j1.2?arch=source&distro=questing`Other threats	Affected =1.2.17-11	Fixed in–
Ubuntu 25.10apache-log4j2`pkg:deb/ubuntu/apache-log4j2?arch=source&distro=questing`Other threats	Affected =2.19.0-2	Fixed in–
Ubuntu 24.04 LTSapache-log4j1.2`pkg:deb/ubuntu/apache-log4j1.2?arch=source&distro=noble`Other threats	Affected =1.2.17-11	Fixed in–

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Users should upgrade Apache Log4j Core to version 2.25.4, which corrects the silent renaming of configuration attributes and restores proper newline escaping and TLS framing behavior. Users of SyslogAppender are not affected and do not need to take action. No other mitigations are specified.

Description

Apache Log4j Core versions 2.21.0 through 2.25.3 have a vulnerability in the Rfc5424Layout related to log injection via CRLF sequences. This is caused by silent renaming of security-relevant configuration attributes, which breaks newline escaping and causes unintended protocol downgrades for certain syslog configurations. The issue does not affect users of SyslogAppender. Upgrading to version 2.25.4 resolves the problem.

Impact

The vulnerability allows an attacker to perform log injection via CRLF sequences in affected versions of Apache Log4j Core when using Rfc5424Layout with certain syslog configurations. This can lead to log forging or manipulation, potentially impacting log integrity and security monitoring. There is no impact on confidentiality or availability. The vulnerability has a CVSS score of 7.5 (high severity).

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 6 Nov 2026, 15:38 UTC

Technical details

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