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

Severity: low (CVSS 2.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-10-15 · updated 2026-10-20
Weakness: CWE-93

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.

Affected products

OpenPrinting cups: before 2.4.20 — fixed in 2.4.20

How to fix

Upgrade to a fixed version: OpenPrinting cups 2.4.20. Check the vendor advisory for mitigations.

References

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