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Vulnerabilities

Vulnerability · CVE-2026-80213

An issue was discovered in the resolv gem before 0.7.2 for Ruby.

Published Aug 27, 2026 · catalog updated Oct 27, 2026 · An issue was discovered

Last checked Oct 28, 2026. A connected source was read within the last 7 days.

Check if you run it

No confirmed exploitation is on record for CVE-2026-80213. EPSS is 0.27%. Act only if a listed version of An issue was discovered is installed.

Gaps on this record

  • The stored product name is a package slug. The name on this page is taken from the title (An issue was discovered).
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
Medium4.0
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.27%
Remediation
Advisory link
Affected products
Alpine:v3.21 ruby · Alpine:v3.22 ruby · Alpine:v3.23 ruby · Alpine:v3.24 ruby

An issue was discovered in the resolv gem before 0.7.2 for Ruby. Resolv::DNS::MessageEncoder wrote a DNS label's length into a single octet without checking its range. A label longer than 255 octets had its length stored modulo 256 but the label data was written unchanged, and thus the bytes on the wire described a different name than the one the application asked to encode. RFC 1035 section 2.3.4 limits a label to 63 octets, and the two high bits of the length octet are reserved for compression pointers. put_string packed the length with put_pack("C", d.length) and put_label used it for labels, and thus any value from 0 to 255 could end up as a label length octet, including the reserved 0x40-0xBF range and the 0xC0-0xFF pointer range. Resolv::DNS::Name.create did not check per-label or total name length either, and thus an attacker-controlled hostname reached the encoder unchanged. An application that resolves an attacker-controlled hostname sends a query whose wire bytes name a domain the attacker chose. A hostname suffix that the application validates against an allowlist becomes padding that never appears on the wire, and thus allowlist and egress checks can be bypassed. The recursive resolver caches the response under the attacker's name, and DNS logs record that name rather than the one the application asked for. A label length whose low octet lands in the 0xC0-0xFF range produces a length octet that conforming parsers read as the start of a compression pointer, with the following attacker-controlled byte as the offset.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • Alpine:v3.21 ruby0 → 3.3.13-r0
  • Alpine:v3.22 ruby0 → 3.4.12-r0
  • Alpine:v3.23 ruby0 → 3.4.12-r0
  • Alpine:v3.24 ruby0 → 3.4.12-r0

How to fix CVE-2026-80213

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-80213. EPSS is 0.27%. Act only if a listed version of An issue was discovered is installed.

Which versions are affected?

Compare what you have installed with 0 → 3.3.13-r0, 0 → 3.4.12-r0. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

No weakness class is stored. EPSS 0.27%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

No public source repository is identified for this product.

Timeline

Detection, updates, and resolution for this record.

  1. Aug 27, 2026 · Trivy Vulnerability DB

    Detected

    An issue was discovered in the resolv gem before 0.7.2 for Ruby. Resolv::DNS::MessageEncoder wrote a DNS label's length into a single octet without checking its range. A label longer than 255 octets had its length stored modulo 256 but the label data was written unchanged, and thus the bytes on the wire described a different name than the one the application asked to encode. RFC 1035 section 2.3.4

  2. Oct 27, 2026 · Trivy Vulnerability DB

    Fix available

    ruby fixed in 3.3.13-r0; ruby fixed in 3.4.12-r0; ruby fixed in 3.4.12-r0; ruby fixed in 3.4.12-r0

  3. Oct 27, 2026 · Trivy Vulnerability DB

    Fix available

    ruby fixed in 3.3.13-r0

  4. Oct 27, 2026 · Trivy Vulnerability DB

    Fix available

    ruby fixed in 3.4.12-r0

  5. Oct 27, 2026 · Trivy Vulnerability DB

    Updated

    An issue was discovered in the resolv gem before 0.7.2 for Ruby. Resolv::DNS::MessageEncoder wrote a DNS label's length into a single octet without checking its range. A label longer than 255 octets had its length stored modulo 256 but the label data was written unchanged, and thus the bytes on the wire described a different name than the one the application asked to encode. RFC 1035 section 2.3.4

Sources

  • CVE.orgVulnerability recordCVE-2026-80213

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-80213

    30-day exploitation probability 0.27%

    first.org
  • Trivy Vulnerability DBPackage advisoryALPINE-CVE-2026-80213

    An issue was discovered in the resolv gem before 0.7.2 for Ruby. Resolv::DNS::MessageEncoder wrote a DNS label's length into a single octet without checking its range. A label longer than 255 octets had its length stored modulo 256 but the label data was written unchanged, and th

    osv.dev

References

Freshness

Last verified in this catalog Oct 28, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.

  • Trivy Vulnerability DBOct 28, 2026
  • FIRST EPSSOct 28, 2026
  • CVE.orgOct 27, 2026