Is CVE-2026-42553 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-42553 being exploited in the wild.

How severe is CVE-2026-42553?

High severity, with a CVSS score of 4, published 27 May 2026.

Which products and versions are affected?

Cinny < 4.10.3; cinny (npm) SEMVER:introduced=0,fixed=4.10.3.

Is there a fix for CVE-2026-42553?

Yes. cinny (npm): upgrade to 4.10.3 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-42553 attacked?

It is attacked over the network, in a web application.

Am I affected by CVE-2026-42553?

Check whether you run Cinny or cinny (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-42553: Cinny access token disclosure via malicious emoji packs

Q: Which products and versions are affected?

Cinny < 4.10.3; cinny (npm) SEMVER:introduced=0,fixed=4.10.3.

Q: Is there a fix for CVE-2026-42553?

Yes. cinny (npm): upgrade to 4.10.3 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

Q: How is CVE-2026-42553 attacked?

It is attacked over the network, in a web application.

Q: Am I affected by CVE-2026-42553?

Check whether you run Cinny or cinny (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-42553 · Severity: high · CVSS 4 · Published 2026-05-27

Cinny is a web-based chat client for the Matrix communication protocol. A vulnerability in how the app handles custom emojis allows a malicious user to steal another person's login token. If a victim opens the emoji picker in a chat room containing a specially crafted emoji pack, their secret access token is automatically sent to the attacker's server, potentially allowing the attacker to take over their account.

Vendors: npm.

Quick answers

Is CVE-2026-42553 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-42553 being exploited in the wild.
How severe is CVE-2026-42553?: High severity, with a CVSS score of 4, published 27 May 2026.
Which products and versions are affected?: Cinny < 4.10.3; cinny (npm) SEMVER:introduced=0,fixed=4.10.3.
Is there a fix for CVE-2026-42553?: Yes. cinny (npm): upgrade to 4.10.3 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-42553 attacked?: It is attacked over the network, in a web application.
Am I affected by CVE-2026-42553?: Check whether you run Cinny or cinny (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

cinny (npm): upgrade to 4.10.3 or later
```
npm install cinny@4.10.3
```

Technical details

Cinny is vulnerable to an information disclosure flaw involving Matrix access tokens. The vulnerability stems from two root causes: first, the EmojiBoard component fails to validate 'pack.meta.avatar' as a proper MXC URL, allowing attackers to inject arbitrary HTTP(S) URLs. Second, the application's service worker automatically attaches the user's Authorization bearer token to any outbound GET request containing specific Matrix media path fragments (download/thumbnail) without verifying if the destination host matches the trusted homeserver. An authenticated attacker with permissions to create room emotes can exploit this by tricking a victim into opening the emoji picker, causing the client to leak the access token to an attacker-controlled server. This is fixed in version 4.10.3.

Affected products

cinnyapp cinny < 4.10.3

Identifiers

CVE-2026-42553
GHSA-j944-w549-3453

Timeline

2026-05-07: disclosed
2026-05-07: advisory
2026-05-07: patched: Fixed in version 4.10.3

References

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