CVE-2025-5994
Description
A cache poisoning flaw was found in Unbound. Resolvers supporting EDNS Client Subnet (ECS) must segregate outgoing queries to accommodate different outgoing ECS information. This issue reopens resolvers to a birthday paradox attack, known as the Rebirthday Attack, which attempts to match the DNS transaction ID with cache non-ECS poisoned replies.
Statement
This vulnerability is considered Important rather than Moderate because it directly compromises the integrity of DNS caching mechanisms in resolvers supporting EDNS Client Subnet (ECS). The flaw allows an attacker to exploit the birthday paradox by generating a high volume of concurrent queries with different ECS values, thereby increasing the chance of a transaction ID collision with a spoofed response. If the resolver fails to properly segregate cache entries by ECS scope, it may accept and cache a malicious non-ECS response, effectively leading to DNS cache poisoning. Unlike typical poisoning attempts that require precise timing or privileged network positions, this attack can be carried out remotely with a high success rate, especially in resolvers that do not correctly isolate ECS queries.
Mitigation
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.
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).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7.5 | N/A | N/A |
| Attack Vector | Network | N/A | N/A |
| Attack Complexity | Low | N/A | N/A |
| Privileges Required | None | N/A | N/A |
| User Interaction | None | N/A | N/A |
| Scope | Unchanged | N/A | N/A |
| Confidentiality | None | N/A | N/A |
| Integrity Impact | High | N/A | N/A |
| Availability Impact | None | N/A | N/A |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Understanding the Weakness (CWE)
Access Control,Integrity
Technical Impact: Bypass Protection Mechanism; Modify Application Data
An attacker could package untrusted data with trusted data to bypass protection mechanisms to gain access to and possibly modify sensitive data.
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