Vulnerability · Published Oct 2, 2026 · Assigned by NCSC.ch
CVE-2026-104721Logback: Incomplete protection against CVE-2026-19880
Medium 6.3
In plain English
A medium-severity path traversal in Logback-classic from QOS.CH Sarl. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 27% of all known vulnerabilities).
Official description
Path-traversal vulnerability in QOS.CH Sarl Logback-classic on Java (logback-classic module) allows path-traversal vulnerability. More specifically, an MDC-based discriminator value flows unsanitized into a nested FileAppender path, letting an attacker who influences that MDC value (e.g. via an HTTP header) create and append log files outside the intended directory. This issue affects Logback-classic: from 0.9.14 through 1.6.4. This vulnerability is similar to CVE-2026-19880 but involves other attack techniques.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | logback | no fix listed | DEBIAN-CVE-2026-104721 |
| Debian:13 | logback | no fix listed | DEBIAN-CVE-2026-104721 |
| Debian:14 | logback | no fix listed | DEBIAN-CVE-2026-104721 |
| Ubuntu:24.04:LTS | logback | no fix listed | UBUNTU-CVE-2026-104721 |
| Ubuntu:26.04:LTS | logback | no fix listed | UBUNTU-CVE-2026-104721 |
| Ubuntu:26.10 | logback | no fix listed | UBUNTU-CVE-2026-104721 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| QOS.CH Sarl | Logback-classic | 0.9.14 – through 1.6.4 |
Weakness: CWE-22 · Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N/S:P/AU:N/RE:M/U:Green