Re: [SECURITY ADVISORY] curl: CVE-2025-10148: predictable WebSocket mask

[Emilio Pozuelo Monfort <pochu27 () gmail com>]

Hi Daniel,

On 10/09/2025 07:54, Daniel Stenberg wrote:
> predictable WebSocket mask
> ==========================
>
> Project curl Security Advisory, September 10 2025 -
> [Permalink](https://curl.se/docs/CVE-2025-10148.html)
>
> VULNERABILITY
> -------------
>
> curl's websocket code did not update the 32 bit mask pattern for each new
> outgoing frame as the specification says. Instead it used a fixed mask that
> persisted and was used throughout the entire connection.
>
> A predictable mask pattern allows for a malicious server to induce traffic
> between the two communicating parties that could be interpreted by an involved
> proxy (configured or transparent) as genuine, real, HTTP traffic with content
> and thereby poison its cache. That cached poisoned content could then be
> served to all users of that proxy.
>
> INFO
> ----
>
> This exact scenario is warned about in the security section of the WebSocket
> RFC 6455 and is the very reason the mask should be updated for every outgoing
> frame.
>
> For this bug to become a real-life problem, the libcurl-using application must
> be communicating through such a (defective) proxy that confuses a WebSocket
> communication for HTTP traffic. Further, to trigger the problem it requires
> the traffic to be done using clear text HTTP / WebSocket (`ws://`) and not
> over TLS (`wss://`).
>
> The Common Vulnerabilities and Exposures (CVE) project has assigned the name
> CVE-2025-10148 to this issue.
>
> CWE-340: Generation of Predictable Numbers or Identifiers
>
> Severity: Low
>
> AFFECTED VERSIONS
> -----------------
>
> - Affected versions: curl 7.86.0 to and including 8.15.0
> - Not affected versions: curl < 7.86.0 and >= 8.16.0
> - Introduced-in: https://github.com/curl/curl/commit/d78e129d50b2d1
>
> WebSocket was considered experimental before 7.86.0 and therefore we do not
> consider earlier versions vulnerable.

From what I can see, websocket support was introduced in 7.86 in [1], and later 
marked as supported/not-experimental in 8.11 [2]. If so, I think the above note 
(also in [3]) should say that it was experimental before 8.11.

Cheers,
Emilio

[1] https://github.com/curl/curl/commit/664249d095275e
[2] https://github.com/curl/curl/commit/d78e129d50b2d1
[3] https://curl.se/docs/CVE-2025-10148.html