CVE-2026-93006 in Dnsmasq
Summary
by MITRE • 10/29/2026
A flaw was found in dnsmasq. The TFTP server can serve the wrong file contents because a recently used transfer cache is not invalidated when a transfer finishes. An attacker on the local network who can request a TFTP file may cause a later client to receive previously cached data instead of the requested file. In PXE network-boot environments this can substitute attacker-chosen boot content for a victim machine.
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Analysis
by VulDB Data Team • 10/29/2026
The vulnerability identified in dnsmasq represents a critical logic error within its Trivial File Transfer Protocol server implementation, specifically concerning how transient state is managed during data transfers. Dnsmasq maintains an internal cache to optimize repeated file requests by storing recently accessed content in memory rather than re-reading from disk or remote sources. However, the flaw arises because this transfer cache entry is not properly invalidated upon the completion of a TFTP transaction. This oversight means that if two different clients request files with similar identifiers or under specific timing conditions where the first client's data remains in the buffer, the second client may inadvertently receive the stale content from the previous session instead of the newly requested file.
From an operational perspective, this behavior introduces significant integrity risks within network infrastructure, particularly in environments relying on automated provisioning and boot processes. The most severe impact is observed in Preboot Execution Environment scenarios where diskless workstations or servers rely on TFTP to retrieve bootloader images from a central server. If an attacker positioned on the local network can trigger a specific file transfer that populates the cache with malicious content, they can subsequently cause legitimate machines requesting their standard boot files to receive this poisoned data instead. This effectively allows for a man-in-the-middle style substitution where the victim machine boots into unauthorized or compromised software provided by the attacker rather than the intended operating system image.
This vulnerability aligns closely with CWE-20 Improper Input Validation, as the application fails to correctly validate and clear internal state based on transaction boundaries, leading to unintended data exposure. Furthermore, in the context of the MITRE ATT&CK framework, this flaw facilitates techniques associated with Taint Shared Components by allowing an attacker to inject malicious payloads into a shared resource that affects multiple victims. It also supports lateral movement or initial access vectors where compromised boot images can lead to full system compromise upon startup. The attack requires local network proximity and does not typically require authentication for basic TFTP operations, making it accessible to any entity with layer 2 connectivity on the affected subnet.
Mitigation strategies should prioritize immediate patching of dnsmasq to versions that include fixes for this cache invalidation logic. Administrators operating PXE environments must also implement network segmentation to isolate boot servers from general user traffic where possible, reducing the attack surface available to potential adversaries. Additionally, verifying the integrity of bootloader images using cryptographic signatures can provide a secondary layer of defense, ensuring that even if cached data is served incorrectly, the client system will reject any unsigned or tampered boot files before execution occurs.