LiveActive security incident?Get immediate response
CVE Record

CVE-2026-33811: Crash when handling long CNAME response in net

When using LookupCNAME with the cgo DNS resolver, a very long CNAME response can trigger a double-free of C memory and a crash.

HighCVSS 7.5Not KEV-listedUpdated
Discuss exposureBack to CVEs
Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

CVE-2026-33811 can crash Go programs that perform CNAME lookups through Go's cgo DNS resolver when a DNS response contains an unusually long CNAME. The business impact is availability: exposed services could terminate unexpectedly if they process attacker-influenced DNS names.

Executive priority

Treat as a high-priority availability fix for Go-based services with DNS lookup functionality, especially public-facing systems. There is no source evidence here of active exploitation, but the remote unauthenticated crash condition justifies prompt patch validation.

Technical view

The Go standard library net package can double-free C memory in LookupCNAME when using the cgo DNS resolver and handling a very long CNAME response. The CVSS 3.1 score is 7.5 because the described impact is remote, unauthenticated denial of service with no confidentiality or integrity impact.

Likely exposure

Most relevant exposure is Go applications that call net.LookupCNAME or dependent code paths while using the cgo DNS resolver. Risk is higher where external users can influence hostnames or DNS lookups. Pure-Go resolver paths are not identified as affected in the provided sources.

Exploitation context

The bundle does not cite CISA KEV listing or confirmed active exploitation. The described trigger is a long CNAME response causing process crash, so assessment should focus on denial-of-service exposure rather than data theft or code execution.

Researcher notes

Key scoping questions are whether LookupCNAME is reachable, whether cgo DNS resolution is active, and whether an attacker can influence DNS answers. The provided sources identify double-free and crash behavior, but do not support claims of code execution or data compromise.

Mitigation direction

  • Apply official Go updates or downstream vendor fixes from referenced advisories.
  • Check GO-2026-4981 for exact affected and fixed Go versions.
  • Prioritize internet-facing services that perform user-influenced CNAME lookups.
  • Apply relevant Red Hat errata where Go packages are supplied by Red Hat.
  • If immediate patching is delayed, reduce externally influenced DNS lookup paths where feasible.

Validation and detection

  • Inventory Go services that use the standard library net package.
  • Review code and dependencies for net.LookupCNAME usage.
  • Determine whether affected services use the cgo DNS resolver.
  • Compare deployed Go versions with GO-2026-4981 and vendor advisories.
  • Confirm patched builds are redeployed for exposed services.
  • Monitor crashes around CNAME lookup handling after remediation.
Prepared
Confidence
high
Sources
12

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cwe · low confidence lookup

CWE-1341: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

Open ATT&CK lookup
cwe · low confidence lookup

CWE-415: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

Open ATT&CK lookup
cve · low confidence lookup

CVE-2026-33811 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

Open ATT&CK lookup
Vulnerability profileCVE Program record
Severity
High
CVSS
7.5 (3.1)
Known Exploited
No
Published

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

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

2CVSS vectors
5Timeline events
2ADP providers
31Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: yesTechnical Impact: partial

CVSS vector scores

2 official scores

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
7.5CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H3.93.6CISA-ADP
7.5CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H3.93.6redhat-SADP

Vulnerability scoring details

Base CVSS 3.1 score

7.5High
CVSS 3.1 vector shape for CVE-2026-33811Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

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

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. ADP timelineredhat-SADP

    Made public.

  3. CVE publishedCVE Program

    The CVE record was published.

  4. ADP timelineredhat-SADP

    Reported to Red Hat.

  5. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
cvssV3_1other:ssvc
redhat-SADPnet: golang: Go net package: Denial of Service via long CNAME response in LookupCNAME
other:Red Hat severity ratingcvssV3_1
  • 2026-05-07T20:01:34.913Z: Reported to Red Hat.
  • 2026-05-07T19:41:19.285Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
Go standard librarynetnet, 0, 1.26.0-0unaffected
Weakness

CWE details

CWE-1341CWE-415

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.

CWE-1341 · source CWE mapping

Multiple Releases of Same Resource or Handle

Multiple Releases of Same Resource or Handle represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs
CWE-415 · source CWE mapping

Double Free

Double Free represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs