Hickory DNS 0.26.0-beta.1 before 0.26.2 Resource Exhaustion DoS via NameServerPool::try_send TC-Retry Loop
Affects hickory-resolver 0.26.0-beta.1 before 0.26.2 when an authoritative server returns truncated (TC=1) responses on every transport. Fixed in 0.26.2.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
- Exploited
- No known exploitation
- Fix
- Fixed in 0.26.2
- Who is exposed
- Not reported
Do first: Upgrade to a fixed version: 0.26.2.
- Published
- Last modified
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 26/100 · provisional
- How many real-world setups can hit the bug, from the vendor's advisory and CISA data. It does not know your setup.What do these mean? →
- Unclear
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
Summary
Hickory DNS hickory-resolver 0.26.0-beta.1 before 0.26.2 contains an unbounded retry loop in NameServerPool::try_send, which re-queues truncated (TC) responses without checking the answering transport or counting iterations. A malicious authoritative server returning TC=1 on every transport keeps the resolver spinning on a persistent TCP connection until the 5-second request deadline expires, causing resource exhaustion.
cve.now Index
- Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
- Exposure17/25No login or user action needed, reachable over the network without a login · Unknown: Advisories don't say whether default setups are affected
- Reach?/20Unknown. No tracked technology or package matched
- Severity8.7/10CVSS 8.7
- No patch0/5No signal
What would change the score
- Would score about 71 if added to CISA KEV
- Would score about 66 if CISA's SSVC rates exploitation active
- Would score about 31 if advisories confirm default setups are exposed
What to do
Upgrade to a fixed version: 0.26.2.
Timeline
- CVE published
- First seen by cve.now
Affected versions
- hickory-dns hickory-dns
From 0.26.0-beta.1 · fixed in 0.26.2
Evidence 2
- Advisory
- Link
Corrections
None so far.
Something wrong on this page? Report an error. Every fix is listed here.
Questions about CVE-2026-123604
Is CVE-2026-123604 being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data
What does this mean?
When an authoritative server sets the TC (truncated) flag on every available transport, the resolver keeps retrying on a persistent TCP connection instead of stopping. This loop uses resources until the 5-second request deadline expires, causing resource exhaustion and denial of service.Source: vulncheck.com, github.com
Which versions are affected by CVE-2026-123604?
hickory-dns: from 0.26.0-beta.1 before 0.26.2.Source: cve.now feed data
Am I affected, and how do I check?
Versions from 0.26.0-beta.1 before 0.26.2 of hickory-resolver (hickory-dns) are affected. The setup involves a resolver querying an authoritative server that returns TC=1 responses on every transport. To check, look at the hickory-resolver version the build uses.Source: vulncheck.com, github.com
How do I fix CVE-2026-123604?
Upgrade hickory-resolver to 0.26.2, which contains the fix. No workaround is listed in the facts.Source: vulncheck.com, github.com