CVE-2026-100404

Status: Awaiting AnalysisMedium (6.5)—

Severity6.5Medium · CVSS 3.1

Exploitation probability0.41 %higher than 34% of CVEs

Active exploitationNonot in the CISA catalog

Public exploitNot knownno public code found

Zulip is an open-source team collaboration tool. In Zulip Server versions through 12.1, guest users can receive new message events for public channels outside their subscriptions. A guest can trigger the issue by registering an event queue with parameters that request messages from an unsubscribed public channel, or an existing event queue can remain affected after the guest's access to the channel is removed. The flaw discloses new public-channel messages to the guest. This issue is fixed in version 12.2.

CVSS

Base score: 6.5
Version: 3.1
Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N

Exploitation probability (EPSS)

Probability of exploitation in the next 30 days: 0.41 %
Percentile among all scored CVEs: 34
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.

ExploitationT1210 Exploitation of Remote Serviceslateral movement85 %
Primary impactT1213 Data from Information Repositoriescollection75 %

Vector AV:N/PR:L/UI:N exige privilegios de invitado (PR:L) y se explota por red, por lo que T1210; el texto indica que se revelan mensajes de canales públicos no suscritos (C:H).

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 Scanning User Training User Account Management Threat Intelligence Program Privileged Account Management Network Segmentation

Affected technologies (1)

⚠ AI-inferred from the description — NVD hasn't analyzed this CVE yet, these aren't verified CPEs.

Zulip — Zulip Server^AI

CWEs

CWE-862

References

Show 5 references

Raw JSON (NVD)

Show

{
  "id": "CVE-2026-100404",
  "cveTags": [],
  "metrics": {
    "cvssMetricV31": [
      {
        "type": "Secondary",
        "source": "security-advisories@github.com",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 6.5,
          "attackVector": "NETWORK",
          "baseSeverity": "MEDIUM",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N",
          "integrityImpact": "NONE",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "availabilityImpact": "NONE",
          "privilegesRequired": "LOW",
          "confidentialityImpact": "HIGH"
        },
        "impactScore": 3.6,
        "exploitabilityScore": 2.8
      }
    ]
  },
  "affected": [
    {
      "source": "security-advisories@github.com",
      "affectedData": [
        {
          "vendor": "zulip",
          "product": "zulip",
          "versions": [
            {
              "status": "affected",
              "version": "< 12.2"
            }
          ]
        }
      ]
    }
  ],
  "published": "2026-10-14T16:17:28.860",
  "references": [
    {
      "url": "https://github.com/zulip/zulip/commit/98659a41cb93d4ce329ea14bb0cdfb4b147500ba",
      "source": "security-advisories@github.com"
    },
    {
      "url": "https://github.com/zulip/zulip/commit/c03db8916456674df3c98614f6f0ef8cd024ef11",
      "source": "security-advisories@github.com"
    },
    {
      "url": "https://github.com/zulip/zulip/pull/39913",
      "source": "security-advisories@github.com"
    },
    {
      "url": "https://github.com/zulip/zulip/releases/tag/12.2",
      "source": "security-advisories@github.com"
    },
    {
      "url": "https://github.com/zulip/zulip/security/advisories/GHSA-5r8f-gq2h-fcgp",
      "source": "security-advisories@github.com"
    }
  ],
  "vulnStatus": "Awaiting Analysis",
  "weaknesses": [
    {
      "type": "Primary",
      "source": "security-advisories@github.com",
      "description": [
        {
          "lang": "en",
          "value": "CWE-862"
        }
      ]
    }
  ],
  "descriptions": [
    {
      "lang": "en",
      "value": "Zulip is an open-source team collaboration tool. In Zulip Server versions through 12.1, guest users can receive new message events for public channels outside their subscriptions. A guest can trigger the issue by registering an event queue with parameters that request messages from an unsubscribed public channel, or an existing event queue can remain affected after the guest's access to the channel is removed. The flaw discloses new public-channel messages to the guest. This issue is fixed in version 12.2."
    }
  ],
  "lastModified": "2026-10-16T16:00:33.533",
  "sourceIdentifier": "security-advisories@github.com"
}