Status: UPDATED | Advisory ID: CVE-2026-34478
| CVE | CVE-2026-34478 |
| CVSS Score / Version | 7.5 (High) / CVSS v3.1 |
| Updated | 2026-09-24 |
| CVSS Vector | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N |
| CVSS Prose | attack vector is network; attack complexity is low; privileges required is none; user interaction is none; scope is unchanged; confidentiality impact is none; integrity impact is high; availability impact is none. |
| Affected products | Apache Log4j |
| Classified as | CWE-117 (Improper Output Neutralization for Logs) |
| Exploitation prediction (EPSS) | 1.19% probability of exploitation in the next 30 days (67% percentile) -- FIRST.org's EPSS model. |
| Vendor | Product | Affected Versions | Patch Status |
|---|---|---|---|
| Apache | Log4j |
| Subsystems | General OT |
| Sectors | Multiple |
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.
Monitor Apache's web page for any future patch releases. See vendor advisory link below.
| Source | Reference |
|---|---|
| NVD | https://nvd.nist.gov/vuln/detail/CVE-2026-34478 |
| CVE | https://www.cve.org/CVERecord?id=CVE-2026-34478 |
| Vendor advisory | https://lists.apache.org/thread/3k1clr2l6vkdnl4cbhjrnt1nyjvb5gwt |