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CVE Record

CVE-2026-27145: Inefficient candidate hostname parsing in crypto/x509

(*x509.Certificate).VerifyHostname previously called matchHostnames in a loop over all DNS Subject Alternative Name (SAN) entries. This caused strings.Split(host, ".") to execute repeatedly on the same input hostname. With a large DNS SAN list, verification costs scaled quadratically based on the number of SAN entries multiplied by the hostname's label count. Because x509.Verify validates hostnames before building the certificate chain, this overhead occurred even for untrusted certificates.

HighCVSS 7.5Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

A malicious or oversized certificate can make affected Go certificate hostname checks consume excessive CPU before trust is even established. The main business risk is service slowdown or denial of service in systems that process untrusted certificates over the network.

Executive priority

Treat as high priority for externally reachable Go services because exploitation can affect availability without authentication. Patch through official Go or OS vendor channels after confirming where affected builds are deployed.

Technical view

In crypto/x509, VerifyHostname repeatedly split the same candidate hostname while looping through DNS SAN entries. Large DNS SAN lists made work scale with SAN count times hostname label count, and x509.Verify performed this before chain building, including for untrusted certificates.

Likely exposure

Exposure is most likely in Go applications built with affected standard library versions that validate peer, uploaded, or otherwise attacker-controlled certificates and hostnames.

Exploitation context

The bundle does not report CISA KEV listing or confirmed active exploitation. The CVSS vector indicates remote, unauthenticated, low-complexity availability impact, but no exploit status is cited.

Researcher notes

The issue is algorithmic complexity rather than memory corruption. Key uncertainty is exact fixed-version coverage from the bundle; rely on Go advisory, Go announcement, and downstream vendor errata for definitive remediation mapping.

Mitigation direction

  • Check Go advisory GO-2026-5037 and Go announcement for fixed releases.
  • Update affected Go toolchains or rebuilt applications following vendor guidance.
  • Apply relevant Red Hat errata for packaged Go components where applicable.
  • Prioritize internet-facing services that validate certificates from untrusted peers.
  • Monitor CPU saturation and TLS or certificate-validation error spikes.

Validation and detection

  • Inventory services and containers built with affected Go standard library versions.
  • Identify code paths using x509.Verify, VerifyHostname, or TLS certificate validation.
  • Check SBOMs and build metadata for Go version provenance.
  • Review exposure to untrusted peer or uploaded certificates.
  • Confirm vendor advisories are applied in runtime images and packages.
Prepared
Confidence
high
Sources
11

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-407: 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.

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cwe · low confidence lookup

CWE-606: 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.

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cve · low confidence lookup

CVE-2026-27145 mapping review

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

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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
22Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: noTechnical 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:H3.93.6redhat-SADP
6.5CVSS 3.1MediumCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H2.24.2CISA-ADP

Vulnerability scoring details

Base CVSS 3.1 score

7.5High
CVSS 3.1 vector shape for CVE-2026-27145Attack 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-SADPcrypto/x509: golang: golang crypto/x509: Denial of Service via excessive processing of DNS SAN entries
other:Red Hat severity ratingcvssV3_1
  • 2026-06-02T23:01:08.992Z: Reported to Red Hat.
  • 2026-06-02T22:01:36.954Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
Go standard librarycrypto/x509crypto/x509, 0, 1.26.0-0unaffected
Weakness

CWE details

CWE-407CWE-606

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

CWE-407 · source CWE mapping

Inefficient Algorithmic Complexity

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

Open CWE intelligenceSame-CWE CVEs
CWE-606 · source CWE mapping

Unchecked Input for Loop Condition

Unchecked Input for Loop Condition represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs