Vulnerability-Lookup

CVE-2026-42553 (GCVE-0-2026-42553)

Vulnerability from cvelistv5 – Published: 2026-05-27 17:27 – Updated: 2026-05-27 18:01

Title

Cinny: Access token disclosure via invalidated emoji pack avatar URL in service worker

Summary

Cinny is a Matrix client. Prior to 4.10.3, A remote authenticated attacker who shares a room with a victim and has permissions to create room emotes (for example in a DM) can cause the victim's client to send their Matrix access token to an attacker-controlled server. This occurs when the victim opens the emoji or sticker picker for the room containing a malicious emote pack. This is caused by an incorrect fallback in EmojiBoard that uses untrusted pack.meta.avatar (user-controlled) without converting/validating it as an MXC URL, allowing arbitrary HTTP(S) URLs to be used. Also, the service worker attaching the user's Authorization bearer token to all outbound GET requests whose URL contains /_matrix/client/v1/media/download or /_matrix/client/v1/media/thumbnail without verifying the request host matches the configured homeserver origin. An attacker-controlled URL containing those path fragments and permissive CORS will receive the victim's Authorization header (access token). This vulnerability is fixed in 4.10.3.

Severity

7.1 (High)


                        
                          CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

SSVC

Exploitation: none Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-05-27 18:01 UTC

CWE

CWE-20 - Improper Input Validation

Assigner

GitHub_M CNA under the mitre root

CNA scorecard C 72/100 over 7763 records in the last 180 days details

References

2 references

URL	Tags
https://github.com/cinnyapp/cinny/security/adviso…	x_refsource_CONFIRM
https://github.com/cinnyapp/cinny/releases/tag/v4.10.3	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version	CPE status
cinnyapp	cinny	Affected: < 4.10.3	guessed

Show details on NVD website

JSON

To clipboard

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}

FKIE_CVE-2026-42553

Vulnerability from fkie_nvd - Published: 2026-05-27 18:16 - Updated: 2026-10-26 11:10

Severity

7.1 (High) - CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/cinnyapp/cinny/releases/tag/v4.10.3
	security-advisories@github.com	https://github.com/cinnyapp/cinny/security/advisories/GHSA-j944-w549-3453

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "product": "cinny",
          "vendor": "cinnyapp",
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    },
    {
      "lang": "es",
      "value": "Cinny es un cliente Matrix. Antes de la versi\u00f3n 4.10.3, un atacante remoto autenticado que comparte una sala con una v\u00edctima y tiene permisos para crear \u2019emotes\u2019 de sala (por ejemplo, en un mensaje directo) puede hacer que el cliente de la v\u00edctima env\u00ede su token de acceso de Matrix a un servidor controlado por el atacante. Esto ocurre cuando la v\u00edctima abre el selector de emojis o pegatinas para la sala que contiene un paquete de \u2019emotes\u2019 malicioso. Esto es causado por un \u2019fallback\u2019 incorrecto en EmojiBoard que utiliza \u2019pack.meta.avatar\u2019 no confiable (controlado por el usuario) sin convertirlo/validarlo como una URL MXC, permitiendo que se utilicen URL HTTP(S) arbitrarias. Adem\u00e1s, el \u2019service worker\u2019 adjunta el token \u2019bearer\u2019 de autorizaci\u00f3n del usuario a todas las solicitudes GET salientes cuya URL contiene /_matrix/client/v1/media/download o /_matrix/client/v1/media/thumbnail sin verificar que el host de la solicitud coincida con el origen del \u2019homeserver\u2019 configurado. Una URL controlada por el atacante que contenga esos fragmentos de ruta y CORS permisivo recibir\u00e1 el encabezado de autorizaci\u00f3n de la v\u00edctima (token de acceso). Esta vulnerabilidad se corrige en la versi\u00f3n 4.10.3."
    }
  ],
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          "vulnConfidentialityImpact": "HIGH",
          "vulnIntegrityImpact": "NONE",
          "vulnerabilityResponseEffort": "NOT_DEFINED"
        },
        "source": "security-advisories@github.com",
        "type": "Secondary"
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-42553",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "role": "CISA Coordinator",
          "timestamp": "2026-05-27T18:01:29.293909Z",
          "version": "2.0.3"
        }
      }
    ]
  },
  "published": "2026-05-27T18:16:22.857",
  "references": [
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/cinnyapp/cinny/releases/tag/v4.10.3"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/cinnyapp/cinny/security/advisories/GHSA-j944-w549-3453"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Deferred",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-20"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Secondary"
    }
  ]
}

GHSA-J944-W549-3453

Vulnerability from github – Published: 2026-05-07 16:40 – Updated: 2026-06-08 23:47

Summary

Cinny vulnerable to access token disclosure via invalidated emoji pack avatar URL in service worker

Details

Impact

A remote authenticated attacker who shares a room with a victim and has permissions to create room emotes (for example in a DM) can cause the victim's client to send their Matrix access token to an attacker-controlled server. This occurs when the victim opens the emoji or sticker picker for the room containing a malicious emote pack.

The root causes are:

(1) an incorrect fallback in EmojiBoard that uses untrusted pack.meta.avatar (user-controlled) without converting/validating it as an MXC URL, allowing arbitrary HTTP(S) URLs to be used; and

(2) the service worker attaching the user's Authorization bearer token to all outbound GET requests whose URL contains /_matrix/client/v1/media/download or /_matrix/client/v1/media/thumbnail without verifying the request host matches the configured homeserver origin. An attacker-controlled URL containing those path fragments and permissive CORS will receive the victim's Authorization header (access token).

Impacted users: anybody using affected Cinny web app versions who opens the emoji/sticker picker in a room containing a malicious emote pack and who is logged in (authenticated).

Patches

Version with fixes: https://github.com/cinnyapp/cinny/releases/tag/v4.10.3

Severity

7.1 (High)


                  
                    CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

Show details on source website

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{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "cinny"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "4.10.3"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-42553"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-20"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-05-07T16:40:52Z",
    "nvd_published_at": "2026-05-27T18:16:22Z",
    "severity": "HIGH"
  },
  "details": "### Impact\nA remote authenticated attacker who shares a room with a victim and has permissions to create room emotes (for example in a DM) can cause the victim\u0027s client to send their Matrix access token to an attacker-controlled server. This occurs when the victim opens the emoji or sticker picker for the room containing a malicious emote pack. \n\nThe root causes are: \n\n(1) an incorrect fallback in EmojiBoard that uses untrusted `pack.meta.avatar` (user-controlled) without converting/validating it as an MXC URL, allowing arbitrary HTTP(S) URLs to be used; and \n\n(2) the service worker attaching the user\u0027s Authorization bearer token to all outbound GET requests whose URL contains `/_matrix/client/v1/media/download` or `/_matrix/client/v1/media/thumbnail` without verifying the request host matches the configured homeserver origin. An attacker-controlled URL containing those path fragments and permissive CORS will receive the victim\u0027s Authorization header (access token). \n\nImpacted users: anybody using affected Cinny web app versions who opens the emoji/sticker picker in a room containing a malicious emote pack and who is logged in (authenticated).\n\n### Patches\nVersion with fixes: https://github.com/cinnyapp/cinny/releases/tag/v4.10.3",
  "id": "GHSA-j944-w549-3453",
  "modified": "2026-06-08T23:47:42Z",
  "published": "2026-05-07T16:40:52Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/cinnyapp/cinny/security/advisories/GHSA-j944-w549-3453"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-42553"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/cinnyapp/cinny"
    },
    {
      "type": "WEB",
      "url": "https://github.com/cinnyapp/cinny/releases/tag/v4.10.3"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Cinny vulnerable to access token disclosure via invalidated emoji pack avatar URL in service worker"
}

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.

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Sightings and recorded dates, grouped by day · UTC

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Following the VTEM framework (Black Hat USA 2015), time to patch starts when the vendor or a coordinator was informed, total time to patch at discovery, and disclosure to patch at public disclosure; vendor response time runs from the report to its acknowledgement. Time to exploit and time unpatched start at the earliest discovery or report, falling back to public disclosure. Unpatched time ends at the first recorded patch, or the calculation time when no patch is recorded. Exploitation to patch shows the interval between those two events; a published proof of concept is a public exploit, not exploitation.

Each result shows its source dates. A negative interval means the end event came first; when date-only inputs leave the order open, the result says so. Date-only inputs are approximate. The earliest evidence wins: KEV report dates and sightings are labelled as such. Records describing another vulnerability are listed but never calculated from, and a PoC alone does not establish exploitation. Missing patch evidence does not prove that no patch exists. Filters below change the event list only.

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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
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CVE-2026-42553 (GCVE-0-2026-42553)

FKIE_CVE-2026-42553

GHSA-J944-W549-3453

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