Vulnerability-Lookup

CVE-2026-30867 (GCVE-0-2026-30867)

Vulnerability from cvelistv5 – Published: 2026-04-02 13:57 – Updated: 2026-04-02 16:23

Title

CocoaMQTT: Denial of Service via Reachable Assertion in `PUBLISH` Packet Parsing

Summary

CocoaMQTT is a MQTT 5.0 client library for iOS and macOS written in Swift. Prior to version 2.2.2, a vulnerability exists in the packet parsing logic of CocoaMQTT that allows an attacker (or a compromised/malicious MQTT broker) to remotely crash the host iOS/macOS/tvOS application. If an attacker publishes the 4-byte malformed payload to a shared topic with the RETAIN flag set to true, the MQTT broker will persist the payload. Any time a vulnerable client connects and subscribes to that topic, the broker will automatically push the malformed packet. The app will instantly crash in the background before the user can even interact with it. This effectively "bricks" the mobile application (a persistent DoS) until the retained message is manually wiped from the broker database. This issue has been patched in version 2.2.2.

Severity ?

5.7 (Medium)


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

CWE

CWE-617 - Reachable Assertion

Assigner

GitHub_M

References

URL

Tags

	https://github.com/emqx/CocoaMQTT/security/adviso…	x_refsource_CONFIRM
	https://github.com/emqx/CocoaMQTT/pull/659	x_refsource_MISC
	https://github.com/emqx/CocoaMQTT/commit/010bca6f…	x_refsource_MISC
	https://github.com/emqx/CocoaMQTT/releases/tag/2.2.2	x_refsource_MISC

Impacted products

	Vendor	Product	Version
	emqx	CocoaMQTT	Affected: < 2.2.2

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-30867

Vulnerability from fkie_nvd - Published: 2026-04-02 14:16 - Updated: 2026-04-07 18:04

Severity ?

5.7 (Medium) - CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:N/A:H
6.5 (Medium) - CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Summary

References

URL	Tags
security-advisories@github.com	https://github.com/emqx/CocoaMQTT/commit/010bca6f61b97d726252f61641d331a2bf82b338	Patch
security-advisories@github.com	https://github.com/emqx/CocoaMQTT/pull/659	Issue Tracking, Patch
security-advisories@github.com	https://github.com/emqx/CocoaMQTT/releases/tag/2.2.2	Release Notes
security-advisories@github.com	https://github.com/emqx/CocoaMQTT/security/advisories/GHSA-r3fr-7m74-q7g2	Exploit, Vendor Advisory

Impacted products

Vendor	Product	Version
emqx	cocoamqtt	*
apple	iphone_os	-
apple	macos	-

JSON

To clipboard

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GHSA-R3FR-7M74-Q7G2

Vulnerability from github – Published: 2026-04-03 21:33 – Updated: 2026-04-03 21:33

Summary

CocoaMQTT: Denial of Service via Reachable Assertion in `PUBLISH` Packet Parsing

Details

A vulnerability exists in the packet parsing logic of CocoaMQTT that allows an attacker (or a compromised/malicious MQTT broker) to remotely crash the host iOS/macOS/tvOS application.

The vulnerability is located in Source/FramePublish.swift during the extraction of the Topic string from the incoming byte array.

When parsing the Variable Header of a PUBLISH frame, the library reads the first two bytes to determine the topicLength. It then adds this length to the current position (pos) and attempts to slice the byte array to extract the string:

if let data = NSString(bytes: [UInt8](bytes[2...(pos-1)]), length: Int(len), encoding: String.Encoding.utf8.rawValue) {
    topic = data as String
}

If a packet is received where the Topic Length evaluates to 0 (e.g., 0x00 0x00), the len variable becomes 0, and pos evaluates to 2.

The slicing logic dynamically calculates bytes[2...(2-1)], which becomes bytes[2...1]. Swift's ClosedRange operator (...) requires the lower bound to be less than or equal to the upper bound. Because 2 is not less than 1, Swift detects an out-of-bounds access attempt and immediately triggers a runtime trap (Fatal error: Range requires lowerBound <= upperBound), crashing the host application.

If an attacker publishes this 4-byte malformed payload to a shared topic with the RETAIN flag set to true, the MQTT broker will persist the payload. Any time a vulnerable client connects and subscribes to that topic, the broker will automatically push the malformed packet. The app will instantly crash in the background before the user can even interact with it. This effectively "bricks" the mobile application (a persistent DoS) until the retained message is manually wiped from the broker database.

Severity ?

5.7 (Medium)


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

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "SwiftURL",
        "name": "CocoaMQTT"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "2.2.2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-30867"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-617"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-04-03T21:33:58Z",
    "nvd_published_at": "2026-04-02T14:16:28Z",
    "severity": "MODERATE"
  },
  "details": "A vulnerability exists in the packet parsing logic of CocoaMQTT that allows an attacker (or a compromised/malicious MQTT broker) to remotely crash the host iOS/macOS/tvOS application.\n\nThe vulnerability is located in `Source/FramePublish.swift` during the extraction of the Topic string from the incoming byte array.\n\nWhen parsing the Variable Header of a `PUBLISH` frame, the library reads the first two bytes to determine the `topicLength`. It then adds this length to the current position (`pos`) and attempts to slice the byte array to extract the string:\n\n```swift\nif let data = NSString(bytes: [UInt8](bytes[2...(pos-1)]), length: Int(len), encoding: String.Encoding.utf8.rawValue) {\n    topic = data as String\n}\n```\n\nIf a packet is received where the Topic Length evaluates to `0` (e.g., `0x00 0x00`), the `len` variable becomes `0`, and `pos` evaluates to `2`.\n\nThe slicing logic dynamically calculates `bytes[2...(2-1)]`, which becomes **`bytes[2...1]`**. Swift\u0027s `ClosedRange` operator (`...`) requires the lower bound to be less than or equal to the upper bound. Because 2 is not less than 1, Swift detects an out-of-bounds access attempt and immediately triggers a runtime trap (`Fatal error: Range requires lowerBound \u003c= upperBound`), crashing the host application.\n\nIf an attacker publishes this 4-byte malformed payload to a shared topic with the `RETAIN` flag set to true, the MQTT broker will persist the payload. Any time a vulnerable client connects and subscribes to that topic, the broker will automatically push the malformed packet. The app will instantly crash in the background before the user can even interact with it. This effectively \"bricks\" the mobile application (a persistent DoS) until the retained message is manually wiped from the broker database.",
  "id": "GHSA-r3fr-7m74-q7g2",
  "modified": "2026-04-03T21:33:58Z",
  "published": "2026-04-03T21:33:58Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/emqx/CocoaMQTT/security/advisories/GHSA-r3fr-7m74-q7g2"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-30867"
    },
    {
      "type": "WEB",
      "url": "https://github.com/emqx/CocoaMQTT/pull/659"
    },
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      "type": "WEB",
      "url": "https://github.com/emqx/CocoaMQTT/commit/010bca6f61b97d726252f61641d331a2bf82b338"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/emqx/CocoaMQTT"
    },
    {
      "type": "WEB",
      "url": "https://github.com/emqx/CocoaMQTT/releases/tag/2.2.2"
    }
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  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "CocoaMQTT: Denial of Service via Reachable Assertion in `PUBLISH` Packet Parsing "
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

Action not permitted

CVE-2026-30867 (GCVE-0-2026-30867)

FKIE_CVE-2026-30867

GHSA-R3FR-7M74-Q7G2

Tags

Sightings

Nomenclature