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CVE-2026-103415

Status: Awaiting AnalysisCritical (9.3)—
Severity9.3Critical · CVSS 4.0
Exploitation probability0.28 %higher than 20% of CVEs
Active exploitationNonot in the CISA catalog
Public exploitNot knownno public code found

When a TLS 1.3 client processes a HelloRetryRequest, it copies the server's cookie into its second ClientHello without checking that the cookie fits in the outgoing packet. Both the length and the contents of that cookie come from the peer, and the write happens before certificate authentication completes, so a malicious or compromised server can overwrite memory past the caller supplied TLS packet buffer without presenting a certificate.

Only the client path is affected.

CVSS

Base score
9.3
Version
4.0
Vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Exploitation probability (EPSS)

Probability of exploitation in the next 30 days
0.28 %
Percentile among all scored CVEs
20
Score date
10/20/2026

EPSS (Exploit Prediction Scoring System, FIRST) estimates how likely a vulnerability is to be exploited in the wild within 30 days. It complements CVSS (impact) and CISA KEV (confirmed exploitation).

ATT&CK techniques

How this vulnerability is exploited and what the attacker gains, in MITRE ATT&CK terms.

Vector AV:N/PR:N/UI:N: un servidor malicioso escribe fuera del búfer (CWE-787) sin certificado. El texto no menciona ejecución de comandos, así que no se asigna T1059.

Inferred by our analysis agent from the official description, CVSS vector and CWE, and checked by a supervisor. May contain errors.

ATT&CK mitigations that cover these techniques

Vulnerability ScanningPrivileged Account ManagementNetwork SegmentationLimit Access to Resource Over NetworkFilter Network TrafficApplication Isolation and Sandboxing

CWEs

References

Show 2 references

Raw JSON (NVD)

Show
{
  "id": "CVE-2026-103415",
  "cveTags": [],
  "metrics": {
    "ssvcV203": [
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        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-103415",
          "role": "CISA Coordinator",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "yes"
            },
            {
              "technicalImpact": "total"
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          "version": "2.0.3",
          "timestamp": "2026-10-16T20:12:26.899295Z"
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    "cvssMetricV40": [
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        "type": "Secondary",
        "source": "emo@eclipse.org",
        "cvssData": {
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          "baseScore": 9.3,
          "Automatable": "NOT_DEFINED",
          "attackVector": "NETWORK",
          "baseSeverity": "CRITICAL",
          "valueDensity": "NOT_DEFINED",
          "vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
          "exploitMaturity": "NOT_DEFINED",
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          "integrityRequirement": "NOT_DEFINED",
          "modifiedAttackVector": "NOT_DEFINED",
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          "vulnAvailabilityImpact": "HIGH",
          "availabilityRequirement": "NOT_DEFINED",
          "modifiedUserInteraction": "NOT_DEFINED",
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          "subConfidentialityImpact": "NONE",
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          "modifiedAttackRequirements": "NOT_DEFINED",
          "modifiedPrivilegesRequired": "NOT_DEFINED",
          "modifiedSubIntegrityImpact": "NOT_DEFINED",
          "modifiedVulnIntegrityImpact": "NOT_DEFINED",
          "vulnerabilityResponseEffort": "NOT_DEFINED",
          "modifiedSubAvailabilityImpact": "NOT_DEFINED",
          "modifiedVulnAvailabilityImpact": "NOT_DEFINED",
          "modifiedSubConfidentialityImpact": "NOT_DEFINED",
          "modifiedVulnConfidentialityImpact": "NOT_DEFINED"
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  "affected": [
    {
      "source": "emo@eclipse.org",
      "affectedData": [
        {
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          "versions": [
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              "version": "0",
              "versionType": "custom",
              "lessThanOrEqual": "6.5.1.202602"
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            {
              "status": "unaffected",
              "version": "6.5.2.202603"
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  "published": "2026-10-14T18:17:19.790",
  "references": [
    {
      "url": "https://github.com/eclipse-threadx/netxduo/security/advisories/GHSA-5pv3-rhf5-gwgq",
      "source": "emo@eclipse.org"
    },
    {
      "url": "https://gitlab.eclipse.org/security/cve-assignment/-/work_items/357",
      "source": "emo@eclipse.org"
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    {
      "lang": "en",
      "value": "When a TLS 1.3 client processes a HelloRetryRequest, it copies the server's cookie into its second ClientHello without checking that the cookie fits in the outgoing packet. Both the length and the contents of that cookie come from the peer, and the write happens before certificate authentication completes, so a malicious or compromised server can overwrite memory past the caller supplied TLS packet buffer without presenting a certificate.\n\n\n\nOnly the client path is affected."
    }
  ],
  "lastModified": "2026-10-16T21:17:13.370",
  "sourceIdentifier": "emo@eclipse.org"
}