CVE-2026-1519 PUBLISHED

Excessive NSEC3 iterations cause high CPU load during insecure delegation validation

Assigner: isc
Reserved: 28.01.2026 Published: 25.03.2026 Updated: 25.03.2026

If a BIND resolver is performing DNSSEC validation and encounters a maliciously crafted zone, the resolver may consume excessive CPU. Authoritative-only servers are generally unaffected, although there are circumstances where authoritative servers may make recursive queries (see: https://kb.isc.org/docs/why-does-my-authoritative-server-make-recursive-queries). This issue affects BIND 9 versions 9.11.0 through 9.16.50, 9.18.0 through 9.18.46, 9.20.0 through 9.20.20, 9.21.0 through 9.21.19, 9.11.3-S1 through 9.16.50-S1, 9.18.11-S1 through 9.18.46-S1, and 9.20.9-S1 through 9.20.20-S1.

Metrics

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CVSS Score: 7.5

Product Status

Vendor ISC
Product BIND 9
Versions Default: unaffected
  • affected from 9.11.0 to 9.16.50 (incl.)
  • affected from 9.18.0 to 9.18.46 (incl.)
  • affected from 9.20.0 to 9.20.20 (incl.)
  • affected from 9.21.0 to 9.21.19 (incl.)
  • affected from 9.11.3-S1 to 9.16.50-S1 (incl.)
  • affected from 9.18.11-S1 to 9.18.46-S1 (incl.)
  • affected from 9.20.9-S1 to 9.20.20-S1 (incl.)

Exploits

We are not aware of any active exploits.

Workarounds

This is not recommended, but disabling DNSSEC (dnssec-validation no;) prevents exploitation of this issue.

Solutions

Upgrade to the patched release most closely related to your current version of BIND 9: 9.18.47, 9.20.21, 9.21.20, 9.18.47-S1, or 9.20.21-S1.

Credits

  • ISC would like to thank Samy Medjahed/Ap4sh for bringing this vulnerability to our attention.

References

Problem Types

  • CWE-606 Unchecked Input for Loop Condition CWE

Impacts

  • If this issue is encountered, the resolver may experience excessive CPU consumption and a sharp decrease in the number of queries per second that it can handle.