CVE-2026-57166 in pjproject
Summary
by MITRE • 09/04/2026
PJSIP is a free and open source multimedia communication library written in C. Prior to commit 4472a31, a stack buffer overflow exists in the PJLIB-UTIL telnet CLI front-end when rendering feedback for an entered command line. Several command-line handling paths write an attacker-influenced amount of data into fixed-size buffers without sufficient bounds checking, so a long command line can overflow them. This affects only applications that enable the telnet CLI front-end (e.g. pj_cli_telnet_create() / --cli-telnet-port). The telnet CLI is an interactive administration interface with no authentication, so any client able to reach it can already issue arbitrary CLI commands. A malformed or overly long command line can overflow a fixed-size stack buffer while rendering command-line feedback, which may lead to application termination. Because reaching this code already requires access to the unauthenticated CLI, the impact beyond that existing access is limited. Applications that do not enable the telnet CLI front-end are not affected. This issue has been patched via commit 4472a31.
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Analysis
by VulDB Data Team • 09/05/2026
PJSIP is a widely utilized open-source multimedia communication library written in C, designed to facilitate voice and video over IP applications. Within this ecosystem, the PJLIB-UTIL component provides utility functions including a telnet command-line interface front-end intended for administrative purposes. This interface allows system administrators or developers to interact with the running application instance via standard telnet protocols. However, prior to commit 4472a31, a critical implementation flaw existed within this specific subsystem that introduced a stack buffer overflow vulnerability during the rendering of feedback for entered commands. The core technical deficiency lies in how command-line handling paths process user input; specifically, several code paths write data influenced by an attacker into fixed-size buffers without performing sufficient bounds checking. When a client submits a command line exceeding the capacity of these internal buffers, the excess data overflows onto adjacent memory locations on the stack, corrupting critical control data such as return addresses or saved frame pointers.
The operational impact of this vulnerability is nuanced due to the specific access requirements for exploitation. The telnet CLI front-end operates without any form of authentication mechanism by default, meaning that any network client capable of establishing a connection to the exposed port can already issue arbitrary commands and interact with the application's internal state. Consequently, an attacker who has reached this code path already possesses significant control over the service. While the stack buffer overflow itself could theoretically lead to remote code execution through careful exploitation techniques such as shellcode injection or return-oriented programming, the practical impact is largely limited to denial of service conditions like application termination or crash in most typical scenarios. The vulnerability does not grant additional privileges beyond what an unauthenticated user already has, but it can destabilize the application by causing crashes during command processing and feedback rendering phases.
From a classification perspective, this flaw aligns with CWE-121, which denotes a stack-based buffer overflow where data is written past the end of a fixed-size buffer on the call stack. This type of vulnerability is particularly dangerous in C applications because it can compromise memory safety guarantees and allow for arbitrary code execution if exploited effectively. In terms of adversary behavior, this relates to ATT&CK technique T1059, Command and Scripting Interpreter, as the vector involves interacting with a command-line interface. Although the primary risk here is service disruption due to the lack of authentication requirements rather than privilege escalation, the underlying memory corruption issue remains a severe security defect that violates fundamental principles of secure coding practices regarding input validation and buffer management.
Mitigation strategies for this vulnerability are straightforward given its specific scope. The most effective remediation is to apply the patch provided in commit 4472a31, which addresses the bounds checking deficiencies within the telnet CLI feedback rendering logic. For organizations that do not require interactive administrative access via Telnet, it is strongly recommended to disable this feature entirely by avoiding calls to pj_cli_telnet_create or omitting the --cli-telnet-port configuration flag during application initialization. If the interface must remain enabled for operational reasons, implementing network-level access controls such as firewall rules or IP whitelisting can restrict connectivity to trusted management networks only. Additionally, deploying intrusion detection systems that monitor for anomalous packet sizes or malformed telnet sessions may provide an additional layer of defense against exploitation attempts targeting this specific buffer overflow condition.