CVE-2026-57196 in Asterisk
Summary
by MITRE • 10/26/2026
Asterisk is an open source private branch exchange and telephony toolkit. Prior to Asterisk 20.20.1, 21.12.3, 22.10.1, 23.4.1 and Certified Asterisk 20.7-cert11, 22.8-cert3, an unauthenticated attacker may use reflected cross-site scripting in `phone provisioning HTTP error pages` to retrieve an authorized user's `AMI session cookie` and impersonate that user when `res_phoneprov` is enabled. The Asterisk HTTP web server, Asterisk Manager Interface (AMI), and AMI access via HTTP must all be enabled; each is disabled by default. The attacker must be able to connect to the HTTP server, which binds only to `127.0.0.1` by default even when enabled, and must convince the authorized user to click a malicious link. This issue is fixed in Asterisk 20.20.1, 21.12.3, 22.10.1, 23.4.1 and Certified Asterisk 20.7-cert11, 22.8-cert3.
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Analysis
by VulDB Data Team • 10/26/2026
Asterisk is a widely deployed open-source software suite that functions as both a private branch exchange (PBX) system and a telephony toolkit, enabling organizations to manage voice communications over IP networks. Within this ecosystem, the Asterisk Manager Interface (AMI) provides an API for external applications to control PBX operations, while the res_phoneprov module facilitates automated provisioning of SIP phones via HTTP. A critical security vulnerability was identified in versions prior to 20.20.1, 21.12.3, 22.10.1, and 23.4.1, as well as specific Certified Asterisk releases, where the HTTP error pages generated by the phone provisioning module were susceptible to reflected cross-site scripting (XSS). This flaw allows an unauthenticated attacker to inject malicious scripts into these error responses, which are then executed in the context of a victim user's browser session when they interact with a manipulated link.
The technical nature of this vulnerability centers on insufficient input validation and output encoding within the HTTP server component responsible for handling phone provisioning requests. When an invalid or malformed request triggers an error response from res_phoneprov, the system incorporates parts of the request directly into the HTML content without proper sanitization. This enables a reflected XSS attack where arbitrary JavaScript code is delivered to the victim's browser. Because the AMI interface often relies on session cookies for authentication and authorization, successfully executing this script allows the attacker to access sensitive client-side data, specifically the AMI session cookie stored in the user's browser. By extracting this cookie, the attacker can impersonate the authorized user, gaining unauthorized administrative control over the PBX system without needing valid credentials or exploiting a separate authentication bypass flaw.
The operational impact of this vulnerability is severe due to the high privileges typically associated with AMI access. An authenticated AMI session grants extensive capabilities, including the ability to place calls, monitor conversations, modify dial plans, and potentially execute commands on the underlying operating system depending on configuration. Consequently, an attacker who successfully exploits this XSS flaw can compromise not only the confidentiality of communications but also the integrity and availability of the telephony infrastructure. This could lead to financial fraud through unauthorized call routing, eavesdropping on sensitive conversations, or denial-of-service attacks by disrupting service for legitimate users. The severity is further amplified in environments where AMI access is exposed beyond localhost, although default configurations typically restrict HTTP binding to 127.0.0.1, limiting the attack surface significantly unless explicitly misconfigured.
From a classification perspective, this vulnerability aligns with CWE-79, which describes Improper Neutralization of Input During Web Page Generation commonly known as Cross-site Scripting (XSS). The exploitation technique involves tricking a user into clicking a malicious link, which corresponds to the ATT&CK tactic of Social Engineering and specifically the sub-technique of Spearphishing Link. While the vulnerability itself is technical in nature, its successful execution relies heavily on social engineering elements to induce the victim to interact with the crafted payload. This highlights the importance of defense-in-depth strategies that combine secure coding practices with user awareness training regarding suspicious links, even within internal corporate networks where trust levels may be assumed higher than they should be for administrative interfaces.
Mitigation requires immediate action by upgrading Asterisk and Certified Asterisk installations to patched versions 20.20.1 or later, 21.12.3 or later, 22.10.1 or later, and 23.4.1 or later, as well as the specified certified releases. For organizations unable to upgrade immediately due to operational constraints, several compensating controls can reduce risk. Administrators should ensure that res_phoneprov is disabled if not actively required for automated phone provisioning. Furthermore, strict adherence to default network configurations is critical; specifically, ensuring that the Asterisk HTTP server and AMI interface are bound exclusively to 127.0.0.1 prevents external attackers from reaching the vulnerable endpoints over the network. Implementing a Web Application Firewall (WAF) with rules capable of detecting and blocking reflected XSS payloads can also provide an additional layer of defense, although it should not be relied upon as the sole mitigation strategy given that WAFs may have bypass vectors or performance implications in high-throughput telephony environments.