# CVE-2026-34479: Apache Log4j 1 to Log4j 2 bridge: silent log event loss in Log4j1XmlLayout due to unescaped XML 1.0 forbidden characters > Attackers can cause log data loss by injecting forbidden XML characters, disrupting downstream log processing systems. - **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-LD36349, CLEANSTART-2026-NL43370, CLEANSTART-2026-RP42469, CLEANSTART-2026-VX38000, CLSA-2026-1779124827, CLSA-2026-1780054786, CLSA-2026-1790941398, DEBIAN-CVE-2026-34479, ECHO-0849-6e0a-d963, GHSA-h383-gmxw-35v2, MINI-22x7-p6vf-g27p, MINI-287m-m9p4-r24r, MINI-2wjj-ghq4-f5hf, MINI-34j6-c8vq-8c95, MINI-35x4-5mwx-2r6x, MINI-394c-3qwp-ggcg, MINI-3hcg-3499-qjxp, MINI-3m82-833v-7wg9, MINI-3w2q-xr78-cxww, MINI-3xxq-9mcg-vfvf, MINI-44m7-m6fv-pc9q, MINI-524w-82ph-qq74, MINI-5p37-6wv7-rgm4, MINI-5xcm-cvv3-r9q5, MINI-69wm-5834-fgrj, MINI-6c4w-hrfp-58w4, MINI-6gg5-wmjx-4rx8, MINI-6hx5-xc42-gg23, MINI-7cv6-g56h-qcmf, MINI-7pf2-584j-v6x3, MINI-7w24-wgpq-mg4j, MINI-8hqc-rmww-jx79, MINI-8mrr-p5g3-vp88, MINI-8pw3-26m5-v8vj, MINI-8r4q-wqwx-gv68, MINI-8x5g-9mch-wvxq, MINI-922j-3cr3-pr7p, MINI-933j-mhch-jh57, MINI-9392-jgff-9rh4, MINI-9c6x-jvxh-jwcv, MINI-9hq3-rxxr-g8jr, MINI-9wm4-3658-vfw5, MINI-cfx8-3mg3-jvx3, MINI-cj25-w84h-9f6g, MINI-g9wv-j9xm-3prr, MINI-gcf3-86w5-7v2x, MINI-ggm8-9xcm-g485, MINI-h452-vjm7-2r5w, MINI-h74h-6jm2-q83v, MINI-hgf4-5fv4-63m7, MINI-hw79-m453-qqmj, MINI-j3vr-hwcr-x86q, MINI-j6hh-g2gf-72x3, MINI-j9g6-54pp-88f9, MINI-jfmc-6jmv-3fxf, MINI-jrg2-r4q8-6wfj, MINI-m5pv-56mj-x754, MINI-m849-g4f5-6996, MINI-mmx9-952w-3f6f, MINI-mv6c-47x7-fmhm, MINI-p63m-wm6r-h6p3, MINI-p99h-9wpv-4444, MINI-pc5c-wj3g-cgvw, MINI-pcvw-rq5m-9gw2, MINI-pjp5-w7p2-79h2, MINI-q4vp-58w9-8fg7, MINI-qrp6-rp44-qx9p, MINI-rj98-7jg3-hm6q, MINI-rr4q-mw43-3qv8, MINI-rvff-2fxj-fg4w, MINI-rvqf-8fvc-fc82, MINI-v8rm-34f2-fc9v, MINI-wpw6-28vq-55x6, MINI-xv5m-fjc9-wp7p, ROOT-APP-MAVEN-CVE-2026-34479, UBUNTU-CVE-2026-34479 ## What is CVE-2026-34479? CVE-2026-34479 is a medium-severity vulnerability in Apache Log4j 1 to Log4j 2 bridge, published on 10 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. ### Official description The Log4j1XmlLayout from the Apache Log4j 1-to-Log4j 2 bridge fails to escape characters forbidden by the XML 1.0 standard, producing malformed XML output. Conforming XML parsers are required to reject documents containing such characters with a fatal error, which may cause downstream log processing systems to drop or fail to index affected records. Two groups of users are affected: * Those using Log4j1XmlLayout directly in a Log4j Core 2 configuration file. * Those using the Log4j 1 configuration compatibility layer with org.apache.log4j.xml.XMLLayout specified as the layout class. Users are advised to upgrade to Apache Log4j 1-to-Log4j 2 bridge version 2.25.4, which corrects this issue. Note: The Apache Log4j 1-to-Log4j 2 bridge is deprecated and will not be present in Log4j 3. Users are encouraged to consult the Log4j 1 to Log4j 2 migration guide https://logging.apache.org/log4j/2.x/migrate-from-log4j1.html , and specifically the section on eliminating reliance on the bridge. Weakness: CWE-116 (Improper Encoding or Escaping of Output) ## Which versions are affected by CVE-2026-34479? 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 2.7 | 2.25.4 | | `org.apache.logging.log4j:log4j-core` | Maven | From 2.7 | 2.25.4 | | `org.apache.logging.log4j:log4j-core` | Maven | From 3.0.0-beta1 to 3.0.0-beta2 | None | | `org.apache.logging.log4j:log4j-core` | Maven | From 3.0.0-beta1 to 3.0.0-beta2 | None | Products: Apache Log4j. ## How do I fix CVE-2026-34479? Upgrade org.apache.logging.log4j:log4j-core to 2.25.4 or later. ## Is CVE-2026-34479 being exploited? There is no known exploitation of CVE-2026-34479 in the wild and no public exploit code. ## Other vulnerabilities in Apache Log4j 1 to Log4j 2 bridge - [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-2026-34479 and fix it if it is affected. What it is: CVE-2026-34479 is a medium-severity vulnerability in Apache Log4j 1 to Log4j 2 bridge, 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-2026-34479 in the wild and no public exploit code. Affected packages and fixed versions: - org.apache.logging.log4j:log4j-core (Maven): affected from 2.7; fixed in 2.25.4 - org.apache.logging.log4j:log4j-core (Maven): affected from 2.7; fixed in 2.25.4 - org.apache.logging.log4j:log4j-core (Maven): affected from 3.0.0-beta1 up to 3.0.0-beta2; no fix listed - org.apache.logging.log4j:log4j-core (Maven): affected from 3.0.0-beta1 up to 3.0.0-beta2; 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-2026-34479/ (Markdown: https://insights.sbomify.com/CVE-2026-34479/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-34479 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-34479 - OSV: https://osv.dev/vulnerability/CVE-2026-34479 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-34479/ Summaries are generated and may contain mistakes; the official description above is the record.