CVE-2026-28810: Predictable DNS Transaction IDs Enable Cache Poisoning in Built-in Resolver

Severity: low (CVSS 3.7 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-04-07 · updated 2026-10-26
Weakness: CWE-340

Description

Generation of Predictable Numbers or Identifiers vulnerability in Erlang/OTP kernel (inet_res, inet_db modules) allows DNS Cache Poisoning. The built-in DNS resolver (inet_res) uses a sequential, process-global 16-bit transaction ID for UDP queries and does not implement source port randomization. Response validation relies almost entirely on this ID, making DNS cache poisoning practical for an attacker who can observe one query or predict the next ID. This conflicts with RFC 5452 recommendations for mitigating forged DNS answers. inet_res is intended for use in trusted network environments and with trusted recursive resolvers. Earlier documentation did not clearly state this deployment assumption, which could lead users to deploy the resolver in environments where spoofed DNS responses are possible. This vulnerability is associated with program files lib/kernel/src/inet_db.erl and lib/kernel/src/inet_res.erl. This issue affects OTP from OTP 17.0 before OTP 28.4.2, OTP 27.3.4.10 and OTP 26.2.5.19, corresponding to kernel from 3.0 before 10.6.2, 10.2.7.4 and 9.2.4.11.

Affected products

Erlang OTP: from 17.0 before 26.2.5.19; from 27.0 before 27.3.4.10; from 28.0 before 28.4.2 — fixed in 26.2.5.19, 27.3.4.10, 28.4.2

How to fix

Upgrade to a fixed version: Erlang OTP 26.2.5.19, 27.3.4.10, 28.4.2. Check the vendor advisory for mitigations.

References

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