CVE-2026-87875 in CUPS
Summary
by MITRE • 09/09/2026
The cupsUTF32ToUTF8() function in CUPS's cups/transcode.c lacks a source-length bound and can read past the end of the source buffer, resulting in a heap out-of-bounds read. This is reachable via SNMP supply-description parsing in backend/snmp-supplies.c with attacker-controlled content.
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Analysis
by VulDB Data Team • 09/09/2026
The vulnerability identified involves a critical memory safety flaw within the Common Unix Printing System (CUPS), specifically located in the cupsUTF32ToUTF8() function found in the source file cups/transcode.c. This function is designed to convert UTF-32 encoded strings into UTF-8 format, a common requirement for handling international character sets in software applications. However, the implementation fails to enforce strict bounds checking on the length of the input data provided by the caller. In standard secure coding practices, any buffer read operation must verify that the requested number of bytes does not exceed the allocated size of the source buffer to prevent reading uninitialized or unrelated memory regions. The absence of this validation mechanism means that if a malicious actor supplies an improperly formatted or truncated UTF-32 string, the conversion routine will continue processing beyond the intended end of the buffer until it encounters invalid data or triggers a segmentation fault.
This technical flaw manifests as a heap out-of-bounds read, which is classified under CWE-125: Out-of-Bounds Read in standard vulnerability taxonomies. The operational impact of this issue is significant because it allows an attacker to potentially leak sensitive information from the process memory space. By carefully crafting input that triggers the over-read condition, an adversary may be able to extract data residing immediately after the target buffer on the heap. This could include pointers, authentication tokens, or other internal state variables used by the CUPS daemon. Furthermore, depending on the specific architecture and compiler optimizations, such out-of-bounds reads can sometimes lead to application crashes, resulting in a denial of service against the printing infrastructure if the process is not configured with robust fault tolerance mechanisms.
The attack vector for this vulnerability is particularly concerning due its accessibility through SNMP supply-description parsing within backend/snmp-supplies.c. Simple Network Management Protocol (SNMP) is widely used in enterprise environments to monitor and manage network devices, including printers. The snmp-supplies.c module processes data received from managed printing equipment via the SNMP protocol. If an attacker can interact with the CUPS daemon over a network interface where SNMP requests are accepted, they can inject maliciously crafted supply description fields into these packets. Because this parsing path is reachable remotely in many configurations, the vulnerability represents a remote code execution or information disclosure risk rather than requiring local physical access to the system.
From an offensive security perspective, this flaw aligns with ATT&CK technique T1046: Network Service Discovery, as it involves interacting with network services to probe for weaknesses, and potentially T1537: Transfer Data to Cloud Account if the leaked data is exfiltrated externally. The lack of source-length bounds checking is a classic example of CWE-20: Improper Input Validation, where the software fails to verify that input meets specified requirements before processing it. This oversight allows malformed inputs to propagate deeper into the application logic without triggering appropriate error handling or boundary checks.
Mitigation strategies for this vulnerability must address both immediate remediation and long-term architectural improvements. The primary fix involves modifying the cupsUTF32ToUTF8() function in cups/transcode.c to include rigorous length validation before initiating any conversion operations. Developers should ensure that the calculated size of the UTF-32 input does not exceed the allocated buffer limits and that all read operations are constrained by these verified bounds. Additionally, integrating static analysis tools into the CI/CD pipeline can help detect similar out-of-bounds access patterns in future code changes. For system administrators unable to immediately patch the software, restricting SNMP access to trusted networks or disabling unnecessary SNMP services can reduce the attack surface and limit exposure to remote exploitation attempts until a secure version of CUPS is deployed.