Hickory DNS Recursive Resolver Denial of Service via Cached Empty Connection Pool
Affects all versions of the hickory-recursor crate and hickory-resolver 0.26.0 before 0.26.2, when a referral has no glue records and name server address queries fail. 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
The recursive resolver in Hickory DNS (all versions of the hickory-recursor crate, and hickory-resolver 0.26.0 before 0.26.2) caches an empty connection pool when it follows a referral with no glue records and all queries for the name servers' IP addresses fail. An attacker able to spoof DNS responses can make these lookups fail, causing all subsequent queries for the affected zone to fail until the cache entry expires or is evicted.
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
through 0.26.0-alpha.1
- hickory-dns hickory-dns
From 0.26.0 · 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-2026-123588
Is CVE-2026-123588 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 the recursive resolver follows a referral with no glue records and every query for the name servers' IP addresses fails, it caches an empty connection pool. Later queries for the affected zone then fail until the cached entry expires or is evicted, which is a denial of service.Source: vulncheck.com, github.com
Which versions are affected by CVE-2026-123588?
hickory-dns: through 0.26.0-alpha.1. hickory-dns: from 0.26.0 before 0.26.2.Source: cve.now feed data
Am I affected, and how do I check?
All versions of the hickory-recursor crate are affected, along with hickory-resolver 0.26.0 before 0.26.2. Check the hickory-recursor and hickory-resolver versions in the project's Cargo.lock or the output of cargo tree to see which versions are in use.Source: vulncheck.com, github.com
How do I fix CVE-2026-123588?
Upgrade hickory-resolver to 0.26.2 or later. The fix is in 0.26.2, and no workaround is listed.Source: vulncheck.com, github.com