# CVE-2026-123571: Hickory DNS integer underflow in TSIG RDATA decoding

Source: https://junglewise.ai/threats/cve-2026-123571-hickory-dns-from-0-26-0-before-0-26-2-contains-an-integer  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-11-08. Updated: 2026-11-08  
License: CC BY 4.0 with a link back

CVE-2026-123571 · Severity: high · CVSS 7.5 · Published 2026-11-08

Hickory DNS is a DNS resolver library used by Rust applications. A flaw in how it processes TSIG (DNS transaction signature) records allows a remote attacker to send a specially crafted DNS record that crashes the application, causing a denial-of-service outage.

Technologies: [Hickory-Dns Hickory DNS](https://junglewise.ai/threats/technologies/hickory-dns). Vendors: [Hickory-Dns](https://junglewise.ai/threats/vendors/hickory-dns).

## Quick answers

**Is CVE-2026-123571 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-123571 being exploited in the wild.

**How severe is CVE-2026-123571?** High severity, with a CVSS score of 7.5, published 8 November 2026.

**Which products and versions are affected?** Hickory-Dns Hickory DNS 0.26.0 before 0.26.2.

**Is there a fix for CVE-2026-123571?** Yes: fixed in 0.26.2. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-123571 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-123571?** Check whether you run Hickory-Dns Hickory DNS at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- Fixed in 0.26.2

## Technical details

An integer underflow vulnerability exists in TSIG RDATA decoding when processing malformed DNS wire format records. A remote attacker can trigger unchecked subtraction that causes a panic in applications compiled with overflow checks enabled (common in dev/debug builds). No authentication or user interaction is required; the attacker simply sends a crafted TSIG record over the network.

## Affected products

- hickory-dns hickory-dns 0.26.0 before 0.26.2

## Timeline

- 2026-09-03: disclosed
- 2026-11-08: advisory

## References

- [https://github.com/hickory-dns/hickory-dns/security/advisories/GHSA-x962-5xwx-fr8x](https://github.com/hickory-dns/hickory-dns/security/advisories/GHSA-x962-5xwx-fr8x)
- [https://www.vulncheck.com/advisories/hickory-dns-from-0.26.0-before-0.26.2-panic-via-tsig-rdata-decoding](https://www.vulncheck.com/advisories/hickory-dns-from-0.26.0-before-0.26.2-panic-via-tsig-rdata-decoding)

## Related threats

- [Hickory DNS resource exhaustion in DoH request buffering](https://junglewise.ai/threats/cve-2026-123577-hickory-dns-from-0-24-0-before-0-26-2-contains-a-resource)
- [Hickory DNS memory exhaustion in DNS-over-QUIC](https://junglewise.ai/threats/cve-2026-123576-hickory-dns-0-24-0-through-0-26-1-contains-a-memory-exhaustion)
- [Hickory DNS resource exhaustion in DNS-over-HTTPS server](https://junglewise.ai/threats/cve-2026-123575-hickory-dns-before-0-26-2-contains-a-resource-exhaustion)