CVE-2026-42553: Cinny Cinny Vulnerable To Access Token Vulnerability

HIGH
Advisory Identifier: GHSA-j944-w549-3453
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CWE-20
Published
Advisory Summary

CVE-2026-42553 is a HIGH cinny vulnerable to access token vulnerability (CWE-20: Improper Input Validation) affecting Cinny libraries in the npm ecosystem. The issue involves cinny vulnerable to access token disclosure via invalidated emoji pack avatar url in service worker. Remediation is available by upgrading affected packages to version 4.10.3.

CVE-2026-42553 at a Glance

CVE Identifier CVE-2026-42553
GHSA Identifier GHSA-j944-w549-3453
Severity HIGH
CVSS v3.1 Base Score N/A
CWE Classification CWE-20: Improper Input Validation
Affected Product Cinny
Package Ecosystem npm
Published Date
Last Updated

How to Fix CVE-2026-42553

To remediate this vulnerability, upgrade all affected Cinny dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

cinny fixed: 4.10.3 
npm install cinny@4.10.3
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

npm ls cinny

How to Check if You Are Affected

To determine whether your Node.js application is affected by CVE-2026-42553, inspect your project dependencies using npm:

npm ls cinny

Analyze the terminal output to locate any version of Cinny in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 4.10.3), your application is affected.

Note: The npm ls cinny command inspects dependencies declared in your package.json and lockfile; it does not perform automated runtime dynamic scanning.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-20: Improper Input Validation, where the product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. In Cinny, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### 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

CVE-2026-42553 Affected Cinny Versions

1 component(s)
Fixed Versions:
4.10.3
Product / Package Ecosystem Affected Versions Fixed Version
cinny
npm/cinny
npm
< 4.10.3
4.10.3

References

GitHub Advisory / Wiki ADVISORY
https://github.com/cinnyapp/cinny/security/advisories/GHSA-j944-w549-3453
NVD — CVE-2026-42553 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-42553
Cinny Source Repository REPOSITORY
https://github.com/cinnyapp/cinny
Cinny Release RELEASE
https://github.com/cinnyapp/cinny/releases/tag/v4.10.3

Frequently Asked Questions

What is CVE-2026-42553?
CVE-2026-42553 is a security vulnerability in Cinny involving Cinny vulnerable to access token disclosure via invalidated emoji pack avatar URL in service worker under CWE-20: Improper Input Validation.
Which Cinny versions are affected?
Affected versions include releases prior to 4.10.3 across affected packages: cinny.
What version fixes CVE-2026-42553?
Upgrading to 4.10.3 (or the latest patched release for your respective branch) resolves the vulnerability.
Is cinny affected?
Yes, cinny is affected in releases prior to 4.10.3. Upgrade your dependency to 4.10.3 or later.
What CWE is associated with CVE-2026-42553?
CVE-2026-42553 is classified under CWE-20: Improper Input Validation (The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.).
How can I check npm dependencies for CVE-2026-42553?
Run the dependency tree command: 'npm ls cinny'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-j944-w549-3453",
  "modified" : "2026-06-08T23:47:42Z",
  "published" : "2026-05-07T16:40:52Z",
  "aliases" : [ "CVE-2026-42553" ],
  "summary" : "Cinny vulnerable to access token disclosure via invalidated emoji pack avatar URL in service worker",
  "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'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. \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'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). \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",
  "severity" : [ {
    "type" : "CVSS_V4",
    "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"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "cinny"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "4.10.3"
      } ]
    } ]
  } ],
  "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"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-20" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-07T16:40:52Z",
    "nvd_published_at" : "2026-05-27T18:16:22Z"
  }
}