CVE-2026-93011
Description
A flaw was found in dnsmasq. After a reduction of internal domain-name buffer sizes, the DNSSEC validator can write a few bytes past a name buffer when converting names to and from DNS wire format. An attacker who can cause the server to validate a crafted DNSSEC response may overwrite a small amount of adjacent heap metadata. DNSSEC support is not compiled in by default and must also be enabled at runtime.
Statement
This vulnerability is rated as Moderate because the overwrite is bounded to 1-3 bytes on a never-freed startup heap chunk, with no demonstrated crash or control-flow impact (availability None rather than Low). Both a compile-time HAVE_DNSSEC gate (off by default) and runtime --dnssec/--trust-anchor flags are required. This is a follow-on issue after the CVE-2026-2291 buffer reduction, not CVE-2026-2291 itself. Current Red Hat dnsmasq packages ship 2.90 or earlier and do not contain the 504-byte buffers introduced in v2.93.
Mitigation
The following measures reduce risk:
1. Do not enable --dnssec or --trust-anchor unless DNSSEC validation is required.
2. Omit -DHAVE_DNSSEC from COPTS (this is the default build).
3. If DNSSEC validation is required, restrict dnsmasq to trusted upstream resolvers.
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 | 5.3 | N/A | 5.3 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | Low | N/A | Low |
| Privileges Required | None | N/A | None |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | None | N/A | None |
| Integrity Impact | Low | N/A | Low |
| Availability Impact | None | N/A | None |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
cve.org: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Red Hat CVSS v3 Score Explanation
Reporter scored 6.5 (A:L). RH scores 5.3 (A:N) because the 1-3 byte overwrite lands on never-freed startup heap metadata and zero crashes were observed in 120 attempts. This is a follow-on to CVE-2026-2291, not CVE-2026-2291 itself.
Understanding the Weakness (CWE)
Integrity
Technical Impact: Modify Memory; Execute Unauthorized Code or Commands
Write operations could cause memory corruption. In some cases, an adversary can modify control data such as return addresses in order to execute unexpected code.
Availability
Technical Impact: DoS: Crash, Exit, or Restart
Attempting to access out-of-range, invalid, or unauthorized memory could cause the product to crash.
Other
Technical Impact: Unexpected State
Subsequent write operations can produce undefined or unexpected results.
Acknowledgements
Red Hat would like to thank Shubham Raj (Causal Security) for reporting this issue.
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