Overview
dnsmasq is affected by multiple memory safety and input validation vulnerabilities, including heap buffer overflows, heap corruption, and code execution flaws. Collectively, these vulnerabilities enable attackers to poison cached DNS records, bypass security controls, crash the dnsmasq process, or under certain conditions, achieve local privilege escalation. dnsmasq has released version 2.92rel2 to fix the vulnerabilities.
Description
dnsmasq is an open-source networking tool that provides DNS forwarding, DHCP, and network boot services for small-to-medium sized networks and home routing devices. It can also function as a DNS resolver, which is the primary exploitation use case for several of the vulnerabilities described below, tracked collectively as CVE-2026-2291, CVE-2026-4890, CVE-2026-4891, CVE-2026-4892, CVE-2026-4893, and CVE-2026-5172.
CVE-2026-2291
dnsmasq’s extract_name() function can be abused to cause a heap buffer overflow, enabling an attacker to inject false DNS cache entries. This could cause DNS queries to be redirected to attacker-controlled IP addresses or result in a Denial of Service (DoS).
CVE-2026-4890
An infinite-loop flaw in the DNSSEC validation of dnsmasq allows remote attackers to cause Denial of Service (DoS) conditions via a crafted DNS packet.
CVE-2026-4891
A heap-based out-of-bounds read vulnerability in the DNSSEC validation of dnsmasq allows remote attackers to leak memory information via a crafted DNS packet.
CVE-2026-4892
A heap-based out-of-bounds write vulnerability in the DHCPv6 implementation of dnsmasq allows local attackers to execute arbitrary code with root privileges via a crafted DHCPv6 packet.
CVE-2026-4893
An information disclosure vulnerability in dnsmasq allows remote attackers to bypass source checks via a crafted DNS packet containing RFC 7871 client-subnet information.
CVE-2026-5172
A buffer overflow vulnerability in dnsmasq’s extract_addresses() function allows attackers to trigger a heap out-of-bounds read and crash dnsmasq by exploiting a malformed DNS response.
Impact
These vulnerabilities collectively pose various risks:
DoS (CVE-2026-2291, CVE-2026-4890, CVE-2026-5172) — dnsmasq may crash or become unresponsive, terminating DNS resolution and affecting dependent services.
Cache Poisoning / Redirection (CVE-2026-2291, CVE-2026-4893) — Attackers may overwrite cache entries or manipulate response routing, enabling the silent redirection of users to malicious domains.
Information Disclosure (CVE-2026-4891, CVE-2026-4893) — Internal memory and network information may be inadvertently exposed.
Local Privilege Escalation (CVE-2026-4892) — A local attacker may execute arbitrary code as root via DHCPv6 manipulation.
Solution
dnsmasq has released version 2.92rel2 to fix the above vulnerabilities, and various vendors have published patches to address individual remediations. A full list of affected vendors and vendor patches can be found in the References section below. This note, as well as the CVE listings, will be updated as additional patches become available.
Acknowledgements
Thank you to the reporters for discovering these vulnerabilities:
* Hugo Martinez (hugomray@gmail.com) – CVE-2026-5172, CVE-2026-2291
* Andrew Fasano (NIST) – CVE-2026-2291
* Royce M (royce@xchglabs.com) – CVE-2026-4893, CVE-2026-4892, CVE-2026-4891, CVE-2026-4890, CVE-2026-2291
* Asim Viladi Oglu Manizada – CVE-2026-4892
* Mattia Ricciardi (mindless) – CVE-2026-2291
This document was written by Christopher Cullen and Molly Jaconski. Special thanks to Simon Kelly of dnsmasq and all participating vendors for their prompt engagement and coordination efforts.

Overview
Casdoor contains an arbitrary file write vulnerability in the implementation of its “Local File System” storage provider. Due to insufficient sanitization of user-supplied paths, an authenticated user with file upload permissions can escape the intended storage directory and write files elsewhere on the target filesystem. The vulnerability allows attackers to bypass Casdoor’s storage sandbox and perform unauthorized actions with the privileges of the Casdoor runtime user.
Description
Casdoor is an open-source identity and access management (IAM) platform and Model Context Protocol (MCP) gateway that provides authentication, single sign-on, and multi-protocol identity services for applications. Internally, it uses its Local File System storage provider to save files to a dedicated $CASDOOR/files/ directory.
During a file upload via the /api/upload-resource endpoint, the Casdoor application determines the target storage filepath by concatenating the user-supplied parameters pathPrefix and fullFilePath. However, values provided for pathPrefix are not properly sanitized, so directory traversal sequences such as ../../ are accepted without any integrity or permission checks beyond those of the OS user running the Casdoor process. The application does not verify that the destination filepath remains inside the dedicated storage directory, and it will create or overwrite any file that the Casdoor process has permission to modify.
CVE-2026-6815 An arbitrary file write vulnerability exists in Casdoor’s Local File System storage provider. Due to insufficient path sanitization, an authenticated attacker with file upload privileges can perform a path traversal attack to create or overwrite arbitrary files elsewhere on the host filesystem, bypassing the application’s intended storage sandbox.
Impact
Successful exploitation enables arbitrary file creation and modification on the host system, which can be used by an attacker to:
* Overwrite any file that is accessible to the Casdoor process.
* Establish persistence by creating scheduled tasks or cron jobs through the filesystem as the Casdoor user.
* Overwrite Casdoor’s backend database file casdoor.db, causing authentication services to fail and locking out all users and dependent applications.
Exploitation of this vulnerability requires the attacker to possess an authenticated session with sufficient permissions to manage storage providers and interact with the resource upload API. Depending on the privileges of the Casdoor service account, this vulnerability may allow escalation from application-level access to full host compromise.
Solution
A pull request has been submitted to the Casdoor repository that implements proper validation of storage paths, available here: https://github.com/casdoor/casdoor/pull/5458 . Otherwise, deployments should limit administrative access and restrict the filesystem permissions of the Casdoor service account. Administrators should avoid using the Local File System provider or disable this service in multi-user or exposed environments.
Acknowledgements
Thanks to Danilo Dell’Orco for researching and reporting this vulnerability. This document was written by Molly Jaconski.

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