CVE-2026-81928
Description
A flaw was found in Net::DNS versions before 1.57 for Perl. An attacker can cause a denial of service (DoS) by sending a specially crafted DNS message with a misplaced Transaction Signature (TSIG) record. When a system using Net::DNS, such as a forwarder or proxy, attempts to re-encode this message, it can lead to unbounded recursion and memory exhaustion, ultimately terminating the process. This vulnerability arises because the sig_data function fails to properly remove TSIG records from all sections of a DNS message, violating RFC 8945 section 5.2 requirements.
Statement
Red Hat has evaluated this vulnerability as having an Important severity impact because unauthenticated remote attackers can induce process crashes and memory exhaustion with minimal network traffic. In Red Hat Enterprise Linux, the perl-Net-DNS package is a DNS resolver library, and the vast majority of consumers act purely as DNS clients that parse replies without re-encoding them, remaining unaffected. Exploitation is restricted to specialized scenarios where custom Perl-based daemons act as DNS proxies, forwarders, or packet relays that re-serialize decoded network packets.
Mitigation
To mitigate this issue, restrict network access to DNS services utilizing `perl-Net-DNS` to trusted clients or internal networks only, thereby limiting exposure. If the DNS service is not required to act as a forwarder or proxy, disable this functionality to prevent the vulnerable code path from being exercised.
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 | 7.5 |
| 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 | None | N/A | None |
| Availability Impact | High | N/A | High |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
cve.org: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
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