CVE-2026-93006
Description
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.
Statement
This vulnerability is rated as Important because cache confusion can substitute PXE boot content, with high integrity and confidentiality impact. Attack vector is adjacent network (TFTP is a LAN service) and attack complexity is high: DNS forwarding overwrites the TFTP cache key, heap reuse of the freed transfer struct is required, and TFTP option negotiation (OACK) clears the cache. Mixed DNS/TFTP deployments are much harder to exploit. TFTP-only PXE servers with DNS disabled are the highest-risk configuration. Current Red Hat dnsmasq packages ship 2.90 or earlier and do not contain the v2.92 TFTP prefetch cache. Products that later ship dnsmasq 2.92 or newer with TFTP compiled in may be affected when TFTP is enabled at runtime.
Mitigation
The following measures reduce risk:
1. If TFTP is not required, do not enable it. Remove --enable-tftp from the dnsmasq configuration.
2. If TFTP is required, restrict it with --tftp-interface=<interface> and avoid running TFTP-only instances that serve untrusted clients on the same network.
3. Compile without TFTP support using COPTS=-DNO_TFTP if TFTP is not needed.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 6.8 | N/A | 6.8 |
| Attack Vector | Adjacent Network | N/A | Adjacent Network |
| Attack Complexity | High | N/A | High |
| Privileges Required | None | N/A | None |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | High | N/A | High |
| Integrity Impact | High | N/A | High |
| Availability Impact | None | N/A | None |
Vector
Red Hat: CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
cve.org: CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
Red Hat CVSS v3 Score Explanation
Reporter scored 8.1. RH scores 6.8: attack complexity High (DNS clobber, heap reuse, no TFTP options) rather than Low, and availability None because the server does not crash.
Understanding the Weakness (CWE)
Integrity,Confidentiality
Technical Impact: Modify Application Data; Read Application Data
If a released resource is subsequently reused or reallocated, then an attempt to use the original resource might allow access to sensitive data that is associated with a different user or entity.
Other,Availability
Technical Impact: Other; DoS: Crash, Exit, or Restart
When a resource is released it might not be in an expected state, later attempts to access the resource may lead to resultant errors that may lead to a crash.
Acknowledgements
Red Hat would like to thank Shubham Raj (Causal Security) for reporting this issue.
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