CVE-2025-40780
Description
A vulnerability was found in BIND resolvers caused by a weakness in the Pseudo Random Number Generator (PRNG). This weakness allows an attacker to potentially predict the source port and query ID used by BIND, enabling cache poisoning attacks. If successful, the attacker can inject malicious DNS responses into the resolver’s cache, causing clients to receive spoofed DNS data. Authoritative servers are generally unaffected, but recursive resolvers are exposed to this risk. Exploitation is remote and does not require user interaction.
Statement
This vulnerability in BIND 9 resolvers caused by a weakness in the Pseudo Random Number Generator (PRNG) used to select the UDP source port and DNS query (transaction) ID. Exploitation requires an attacker to correctly predict both values and race the legitimate authoritative response with a spoofed packet to perform cache poisoning. While the PRNG weakness reduces entropy and makes prediction feasible under certain conditions, this still requires precise timing, on-path or spoofing capabilities, and targeting of recursive resolvers.
The impact is limited to resolver cache integrity; it does not allow remote code execution, privilege escalation, or direct compromise of the BIND server itself. Authoritative servers are not affected. Additionally, operational mitigations such as DNSSEC validation, access control restricting recursion, and network-level packet filtering reduce real-world exploitability. No active exploits have been observed in the wild.
Because exploitation is non-trivial, requires network-level spoofing and precise timing, and only affects cache integrity without server compromise, the vulnerability is considered Important rather than Critical.
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.
To reduce risk, restrict recursive queries to trusted or internal networks only, and apply rate limiting or firewall rules to prevent excessive or repetitive requests. Enabling DNSSEC validation helps reject forged records, while isolating recursive resolvers from authoritative servers limits the impact of potential cache poisoning. Active monitoring of CPU usage, query volume, and cache anomalies can provide early warning of abuse or attacks.
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 | 8.6 | N/A | 8.6 |
| 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 | Changed | N/A | Changed |
| Confidentiality | None | N/A | None |
| Integrity Impact | High | N/A | High |
| Availability Impact | None | N/A | None |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:N
cve.org: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:N
Understanding the Weakness (CWE)
Access Control
Technical Impact: Bypass Protection Mechanism
If a PRNG is used for authentication and authorization, such as a session ID or a seed for generating a cryptographic key, then an attacker may be able to easily guess the ID or cryptographic key and gain access to restricted functionality.
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