CVE-2023-27598 in OpenSIPS
Summary
by MITRE • 03/15/2023
OpenSIPS is a Session Initiation Protocol (SIP) server implementation. Prior to versions 3.1.7 and 3.2.4, sending a malformed `Via` header to OpenSIPS triggers a segmentation fault when the function `calc_tag_suffix` is called. A specially crafted `Via` header, which is deemed correct by the parser, will pass uninitialized strings to the function `MD5StringArray` which leads to the crash. Abuse of this vulnerability leads to Denial of Service due to a crash. Since the uninitialized string points to memory location `0x0`, no further exploitation appears to be possible. No special network privileges are required to perform this attack, as long as the OpenSIPS configuration makes use of functions such as `sl_send_reply` or `sl_gen_totag` that trigger the vulnerable code. This issue has been fixed in versions 3.1.7 and 3.2.4.
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Analysis
by VulDB Data Team • 03/16/2023
The vulnerability identified as CVE-2023-27598 affects OpenSIPS, a widely deployed Session Initiation Protocol (SIP) server implementation that serves as a critical component in VoIP infrastructure. This issue represents a classic buffer overflow scenario within the SIP processing pipeline, specifically targeting the handling of malformed Via headers that are processed by the server's internal parsing mechanisms. The vulnerability exists in versions prior to 3.1.7 and 3.2.4, making a substantial portion of deployed OpenSIPS installations susceptible to this attack vector that can be leveraged for denial of service exploitation.
The technical flaw manifests when a maliciously crafted Via header is sent to the OpenSIPS server, where the parser correctly processes the header but fails to properly initialize certain string variables before passing them to downstream functions. Specifically, the `calc_tag_suffix` function receives uninitialized strings that are subsequently passed to the `MD5StringArray` function, which attempts to process these uninitialized memory references. This improper initialization leads to a segmentation fault when the system attempts to access memory locations that have not been properly allocated or initialized, causing the server process to crash and terminate unexpectedly.
The operational impact of this vulnerability is significant within the context of VoIP infrastructure security, as it enables a remote attacker to trigger a denial of service condition without requiring any special network privileges or authentication credentials. The attack can be executed against any OpenSIPS server configuration that utilizes functions such as `sl_send_reply` or `sl_gen_totag`, which are commonly used in SIP communication flows. These functions serve as triggers for the vulnerable code path, meaning that legitimate SIP traffic processing can inadvertently activate the crash condition, potentially disrupting voice communication services for extended periods.
The vulnerability aligns with CWE-457: Use of Uninitialized Variable, which is classified under the broader category of software weaknesses that can lead to unpredictable behavior and system instability. From an adversarial perspective, this issue maps to ATT&CK technique T1499.004: Endpoint Denial of Service, where the attacker leverages application-level vulnerabilities to cause system instability. The fact that the uninitialized string points to memory location 0x0 indicates a particularly straightforward exploitation path where the system attempts to dereference a null pointer, which is a well-documented pattern for causing segmentation faults in C-based applications. While the vulnerability does not appear to enable further exploitation beyond the initial crash, the denial of service aspect alone represents a significant security concern for mission-critical communication infrastructure.
The fix implemented in versions 3.1.7 and 3.2.4 addresses the root cause by ensuring proper initialization of string variables before they are passed to cryptographic functions. This remediation follows standard secure coding practices that emphasize the importance of initializing all variables and memory structures before use. Organizations running OpenSIPS servers should prioritize immediate deployment of these patched versions to eliminate the risk of service disruption, particularly in environments where SIP-based communication services are critical for business operations. The vulnerability demonstrates the importance of thorough input validation and proper memory management in network infrastructure software, where even seemingly benign parsing operations can lead to critical system instability.