How severe is CVE-2026-61666?

No CVSS score has been assigned to CVE-2026-61666 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-61666?

CVE-2026-61666 affects the following packages: websocket-driver (RubyGems). Ecosystems affected: RubyGems.

How do I fix CVE-2026-61666?

Update websocket-driver to 0.8.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-61666 is resolved across your whole dependency graph.

How do I detect CVE-2026-61666 in my RubyGems dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for websocket-driver, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-61666 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is CVE-2026-61666 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-61666 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-61666?

CVE-2026-61666 has an EPSS (Exploit Prediction Scoring System) score of 0.4%, placing it in the 38th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-61666?

CVE-2026-61666 is classified as CWE-248 (CWE-248). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-61666 published, and has it been updated?

CVE-2026-61666 was published on August 17, 2026 and was last updated on October 21, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

💎 RubyGems

Not in CISA KEV

CVE-2026-61666 — websocket-driver

Fix: faye/websocket-driver-ruby@7d6fd87

CVE-2026-61666 is a CWE-248 vulnerability in websocket-driver. A fix is available for websocket-driver — see the affected versions and patch details below.

websocket-driver: Denial of service via malformed Host header

Also known asGHSA-2x63-gw47-w4mm

Published

Aug 17, 2026

Updated

Oct 21, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 23, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-61666.

EPSS Exploitation Probability

via FIRST.org ↗

0.4%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs38th percentile — riskier than 38% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected

💎websocket-driver

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects RubyGems packages — download data is not available via public APIs for these ecosystems.

Description

Impact

If this library is used to implement a WebSocket server on top of a TCP server, by using the WebSocket::Driver.server() method, then a client can cause the server to crash by sending a Host header that is not a valid host[:port] string. When this happens, a URI::InvalidURIError exception is raised which is not caught, and this can cause the server process to crash if the application does not catch the error from the parse() method itself.

Patches

The issue has been patched in version 0.8.2 by making the request parser catch URI::InvalidURIError and enter an error state if the Host header is malformed. This means the request is considered invalid and should not establish a WebSocket connection.

Workarounds

No known workarounds exist.

Acknowledgements

This issue was discovered and reported by Pranjali Thakur, DepthFirst Security Research Team.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
💎RubyGems	`websocket-driver`	all versions	0.8.2`bundle update websocket-driver --conservative`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for websocket-driver, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update websocket-driver to 0.8.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-61666 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatImportant

Important: A denial of service flaw was found in the `websocket-driver` Ruby gem. A remote attacker can send a specially crafted, malformed Host header to a WebSocket server utilizing this gem, causing the server to crash due to an unhandled exception.

Workaround published by Red Hat

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.

Source: Red Hat security advisory for CVE-2026-61666 (CC BY 4.0)

Frequently Asked Questions

### Impact If this library is used to implement a WebSocket server on top of a TCP server, by using the `WebSocket::Driver.server()` method, then a client can cause the server to crash by sending a `Host` header that is not a valid `host[:port]` string. When this happens, a `URI::InvalidURIError` exception is raised which is not caught, and this can cause the server process to crash if the application does not catch the error from the `parse()` method itself. ### Patches The issue has been patched in version 0.8.2 by making the request parser catch `URI::InvalidURIError` and enter an error

O3 Security · Impact-Aware SCA

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