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CVE-2026-91156

Status: DeferredHigh (7.5)—
Severity7.5High · CVSS 3.1
Exploitation probability0.48 %higher than 40% of CVEs
Active exploitationNonot in the CISA catalog
Public exploitNot knownno public code found

Discourse is an open-source discussion platform. Prior to 2026.9.0, 2026.8.1, 2026.7.3, and 2026.1.9, MessageBus audience calculation could deliver messages from a read-restricted category chat channel to an authenticated user who could view the category but was not allowed to use Chat under the site's group restrictions. The publication path bounded events by category visibility without also enforcing Chat eligibility, exposing live and recent message content available in the MessageBus backlog. The issue does not permit retrieval of the channel's full history through the Chat API and does not permit message creation or modification. This issue is fixed in versions 2026.9.0, 2026.8.1, 2026.7.3, and 2026.1.9.

CVSS

Base score
7.5
Version
3.1
Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Exploitation probability (EPSS)

Probability of exploitation in the next 30 days
0.48 %
Percentile among all scored CVEs
40
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 y descripción: mensajes de canales de chat restringidos se entregan a usuarios sin permiso de Chat, exponiendo contenido en vivo y reciente (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 ScanningUser TrainingUser Account ManagementPrivileged Account ManagementNetwork SegmentationMulti-factor Authentication

Affected technologies (1)

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

Discourse — DiscourseAI

CWEs

References

Show 5 references

Raw JSON (NVD)

Show
{
  "id": "CVE-2026-91156",
  "cveTags": [],
  "metrics": {
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-91156",
          "role": "CISA Coordinator",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "yes"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "version": "2.0.3",
          "timestamp": "2026-10-14T17:41:47.693023Z"
        }
      }
    ],
    "cvssMetricV31": [
      {
        "type": "Secondary",
        "source": "security-advisories@github.com",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 7.5,
          "attackVector": "NETWORK",
          "baseSeverity": "HIGH",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N",
          "integrityImpact": "NONE",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "availabilityImpact": "NONE",
          "privilegesRequired": "NONE",
          "confidentialityImpact": "HIGH"
        },
        "impactScore": 3.6,
        "exploitabilityScore": 3.9
      }
    ]
  },
  "affected": [
    {
      "source": "security-advisories@github.com",
      "affectedData": [
        {
          "vendor": "discourse",
          "product": "discourse",
          "versions": [
            {
              "status": "affected",
              "version": "< 2026.1.9"
            },
            {
              "status": "affected",
              "version": ">= 2026.7.0-latest, < 2026.7.3"
            },
            {
              "status": "affected",
              "version": ">= 2026.8.0-latest, < 2026.8.1"
            },
            {
              "status": "affected",
              "version": ">= 2026.9.0-latest, < 2026.9.0"
            }
          ]
        }
      ]
    }
  ],
  "published": "2026-10-14T16:17:56.310",
  "references": [
    {
      "url": "https://github.com/discourse/discourse/commit/046fb7bfd68a5b95e63dda88c3c73877c5cf9d5e",
      "source": "security-advisories@github.com"
    },
    {
      "url": "https://github.com/discourse/discourse/commit/87b31bf60a7827f075634254379a1dcbaba409cb",
      "source": "security-advisories@github.com"
    },
    {
      "url": "https://github.com/discourse/discourse/commit/ba74bb404ab4439f5b1f0204e848d62099db8ae1",
      "source": "security-advisories@github.com"
    },
    {
      "url": "https://github.com/discourse/discourse/commit/cac1f26f275cec3dc1dd51dfdac2b3d1a4ec50f8",
      "source": "security-advisories@github.com"
    },
    {
      "url": "https://github.com/discourse/discourse/security/advisories/GHSA-gh4f-qr62-vx8q",
      "source": "security-advisories@github.com"
    }
  ],
  "vulnStatus": "Deferred",
  "weaknesses": [
    {
      "type": "Secondary",
      "source": "security-advisories@github.com",
      "description": [
        {
          "lang": "en",
          "value": "CWE-862"
        }
      ]
    }
  ],
  "descriptions": [
    {
      "lang": "en",
      "value": "Discourse is an open-source discussion platform. Prior to 2026.9.0, 2026.8.1, 2026.7.3, and 2026.1.9, MessageBus audience calculation could deliver messages from a read-restricted category chat channel to an authenticated user who could view the category but was not allowed to use Chat under the site's group restrictions. The publication path bounded events by category visibility without also enforcing Chat eligibility, exposing live and recent message content available in the MessageBus backlog. The issue does not permit retrieval of the channel's full history through the Chat API and does not permit message creation or modification. This issue is fixed in versions 2026.9.0, 2026.8.1, 2026.7.3, and 2026.1.9."
    }
  ],
  "lastModified": "2026-10-14T18:19:33.973",
  "sourceIdentifier": "security-advisories@github.com"
}