# CVE-2026-34478: Apache Log4j Core: Log injection in Rfc5424Layout due to silent configuration incompatibility > Attackers can inject CRLF sequences into logs via Rfc5424Layout due to silent configuration renames, affecting users with specific syslog setups. - **Severity:** Medium 6.9 (`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`) - **Exploited in the wild:** Not known - **Login needed:** Not needed - **Attackable:** Over the internet - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 10 Apr 2026 - **Updated:** 10 Apr 2026 - **Also known as:** CLEANSTART-2026-CP64029, CLEANSTART-2026-DZ37385, CLEANSTART-2026-GW86512, CLEANSTART-2026-ZG68891, CLEANSTART-2026-ZR66277, ECHO-d811-dae2-2041, GHSA-445c-vh5m-36rj, MINI-26xc-8vr3-f3fg, MINI-2r54-3prx-9jh3, MINI-2vv6-9h26-723j, MINI-3gp9-x68q-ghv2, MINI-4f39-xgm4-mh8x, MINI-4v9c-p23j-wfq8, MINI-5cgq-gvph-69h2, MINI-5f3g-pxv5-9fp7, MINI-5f68-qp9h-jm4p, MINI-65j6-798c-5wvm, MINI-65w8-vm9x-whh7, MINI-682j-hww5-hg74, MINI-6g38-pm39-wrxr, MINI-7p8v-pcx8-ppc9, MINI-7pp3-86vf-grj2, MINI-856j-g8f6-wcq6, MINI-8gwp-78hv-c82c, MINI-8r9m-7g9m-gjpp, MINI-8rgw-fqhq-x5cc, MINI-93xh-cq2w-3c85, MINI-9g2g-j229-mf24, MINI-9mw4-rxjv-88hx, MINI-ccmj-w57x-22r8, MINI-f44g-wfgp-php8, MINI-f49v-36vg-4g4f, MINI-f6xg-5rmv-6x82, MINI-f9hp-q6qj-hrfr, MINI-fmf3-j6ch-r275, MINI-g5gr-qfcj-j5p9, MINI-g6j4-qp2v-938x, MINI-g7fc-xgfq-2hv2, MINI-h4gc-m9jp-2g7j, MINI-h85v-x485-4jv4, MINI-h8j5-hv3q-6vcr, MINI-hgf6-jcwj-x76v, MINI-hqf3-j5pq-fmvq, MINI-j2p4-6hrx-qw3p, MINI-j595-j9g2-4r74, MINI-jjq2-pgqw-h743, MINI-jwfq-prgm-w3v6, MINI-m9mv-3298-99fr, MINI-mf3q-m5f3-p7wv, MINI-mf4v-fg2p-vqj6, MINI-mj9v-xc64-pc5j, MINI-p257-9h6w-64mq, MINI-p68x-2c4r-gfq6, MINI-p75m-m7m8-j4rr, MINI-p9vg-28q5-3x55, MINI-pcr2-qxm4-9q8w, MINI-pmfv-fv53-qjwg, MINI-q3r8-fhw2-4xgh, MINI-q839-cpcx-3pm2, MINI-rr49-9pp7-q4p8, MINI-vcwv-r5j3-rq77, MINI-vp58-g7p9-hr4x, MINI-w27m-xwwj-mj8p, MINI-wqrq-hwv6-q872, MINI-wr3w-3xcq-v7m4, MINI-x672-vw6c-p392, MINI-xfw5-pvqf-x3q7, MINI-xg67-372m-9rmf, MINI-xh2m-5c7f-gfcq, MINI-xmc7-753c-qvwh, MINI-xpr8-mc5g-rqx8, MINI-xwgh-6375-pvwh, MINI-xxcj-w7qr-ccqg, ROOT-APP-MAVEN-CVE-2026-34478, UBUNTU-CVE-2026-34478 ## What is CVE-2026-34478? CVE-2026-34478 is a medium-severity vulnerability in Apache Log4j Core, published on 10 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. ### Official 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. Weakness: CWE-684 (Incorrect Provision of Specified Functionality), CWE-117 (Improper Output Neutralization for Logs) ## Which versions are affected by CVE-2026-34478? 4 open source packages ship an affected version, including org.apache.logging.log4j:log4j-core. It affects 1 product. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `org.apache.logging.log4j:log4j-core` | Maven | From 2.21.0 | 2.25.4 | | `org.apache.logging.log4j:log4j-core` | Maven | From 2.21.0 | 2.25.4 | | `org.apache.logging.log4j:log4j-core` | Maven | From 3.0.0-beta1 to 3.0.0-beta3 | None | | `org.apache.logging.log4j:log4j-core` | Maven | From 3.0.0-beta1 to 3.0.0-beta3 | None | Products: Apache Log4j. ## How do I fix CVE-2026-34478? Upgrade org.apache.logging.log4j:log4j-core to 2.25.4 or later. ## Is CVE-2026-34478 being exploited? There is no known exploitation of CVE-2026-34478 in the wild and no public exploit code. ## Other vulnerabilities in Apache Log4j Core - [CVE-2021-44228](https://insights.sbomify.com/CVE-2021-44228/): Apache Log4j2 Remote Code Execution (critical 10.0, exploited in the wild) - [CVE-2021-45046](https://insights.sbomify.com/CVE-2021-45046/): Apache Log4j2 Deserialization of Untrusted Data (critical 9.0, exploited in the wild) - [CVE-2022-23305](https://insights.sbomify.com/CVE-2022-23305/): SQL injection in JDBC Appender in Apache Log4j V1 (critical 9.8) - [CVE-2017-5645](https://insights.sbomify.com/CVE-2017-5645/): Deserialization of Untrusted Data in Log4j (critical 9.8) - [CVE-2022-23302](https://insights.sbomify.com/CVE-2022-23302/): Deserialization of untrusted data in JMSSink in Apache Log4j 1.x (high 8.8) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2026-34478 and fix it if it is affected. What it is: CVE-2026-34478 is a medium-severity vulnerability in Apache Log4j Core, published on 10 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. Exploitation: There is no known exploitation of CVE-2026-34478 in the wild and no public exploit code. Affected packages and fixed versions: - org.apache.logging.log4j:log4j-core (Maven): affected from 2.21.0; fixed in 2.25.4 - org.apache.logging.log4j:log4j-core (Maven): affected from 2.21.0; fixed in 2.25.4 - org.apache.logging.log4j:log4j-core (Maven): affected from 3.0.0-beta1 up to 3.0.0-beta3; no fix listed - org.apache.logging.log4j:log4j-core (Maven): affected from 3.0.0-beta1 up to 3.0.0-beta3; no fix listed Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2026-34478/ (Markdown: https://insights.sbomify.com/CVE-2026-34478/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-34478 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-34478 - OSV: https://osv.dev/vulnerability/CVE-2026-34478 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-34478/ Summaries are generated and may contain mistakes; the official description above is the record.