CUPS 2.4.20 Control-Char Injection via Fax Queue
CVE-2026-55467 Published on October 15, 2026
CUPS fax option values bypass the CVE-2026-34980 control-character sanitizer (incomplete fix)
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.
Vulnerability Analysis
CVE-2026-55467 can be exploited with local system access, and requires small amount of user privileges. This vulnerability is consided to have a high level of attack complexity. Public availability of a proof of concept (POC) exploit exists for CVE-2026-55467. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality and integrity, and a small impact on availability.
Weakness Types
What is a CRLF Injection Vulnerability?
The software uses CRLF (carriage return line feeds) as a special element, e.g. to separate lines or records, but it does not neutralize or incorrectly neutralizes CRLF sequences from inputs.
CVE-2026-55467 has been classified to as a CRLF Injection vulnerability or weakness.
What is a Code Injection Vulnerability?
The software constructs all or part of a code segment using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the syntax or behavior of the intended code segment.
CVE-2026-55467 has been classified to as a Code Injection vulnerability or weakness.
Improper Neutralization of Escape, Meta, or Control Sequences
The software receives input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could be interpreted as escape, meta, or control character sequences when they are sent to a downstream component. As data is parsed, an injected/absent/malformed delimiter may cause the process to take unexpected actions.
Products Associated with CVE-2026-55467
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