GO-2026-5027 CVE-2026-42502
Invoking incorrect handling of HTML elements in foreign content in golang.org/x/net/html
Medium
Go
- Severity
- 6.1 / 10
- Medium · CVSS 3.1
- Exploit chance (EPSS)
- 0.22%
- Chance of exploitation in the next 30 days. Higher than 12.99% of scored vulnerabilities.
- Known exploited
- No
- Not in CISA's catalog
- Weakness
- CWE-1021 Improper Restriction of Rendered UI Layers or Frames
- Fix
0.55.0- Upgrade golang.org/x/net to this version or later
Description
Parsing arbitrary HTML which is then rendered using Render can result in an unexpected HTML tree. This can be leveraged to execute XSS attacks in applications that attempt to sanitize input HTML before rendering.
Affected versions
Go
| Package | Vulnerable | Fixed in |
|---|---|---|
| golang.org/x/net | < 0.55.0 |
0.55.0 |
How to fix
Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.
golang.org/x/net Go → 0.55.0
- go
go get golang.org/x/net@v0.55.0 && go mod tidy
Severity breakdown
CVSS 3.1 6.1
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- Required
- Scope
- Changed
- Confidentiality
- Low
- Integrity
- Low
- Availability
- None
Weakness
CWE-1021: Improper Restriction of Rendered UI Layers or Frames
The web application does not restrict or incorrectly restricts frame objects or UI layers that belong to another application or domain.
How to prevent it
- Implementation: The use of X-Frame-Options allows developers of web content to restrict the usage of their application within the form of overlays, frames, or iFrames. The developer can indicate from which domains can frame the content. The concept of X-Frame-Options is well documented, but implementation of this protection mechanism is in development to cover gaps. There is a need for allowing frames from multiple domains.
- Implementation: A developer can use a "frame-breaker" script in each page that should not be framed. This is very helpful for legacy browsers that do not support X-Frame-Options security feature previously mentioned. It is also important to note that this tactic has been circumvented or bypassed. Improper usage of frames can persist in the web application through nested frames. The "frame-breaking" script does not intuitively account for multiple nested frames that can be presented to the user.
- Implementation: This defense-in-depth technique can be used to prevent the improper usage of frames in web applications. It prioritizes the valid sources of data to be loaded into the application through the usage of declarative policies. Based on which implementation of Content Security Policy is in use, the developer should use the "frame-ancestors" directive or the "frame-src" directive to mitigate this weakness. Both directives allow for the placement of restrictions when it comes to allowing embedded content.
- Implementation: In addition to frames or iframes as previously mentioned, the web application is expected to place restrictions on whether it is allowed to be rendered within objects, embed, or applet elements.
References
Advisories
Fixes and patches
Issue reports
Other links
Timeline
- Published
- Last updated by the source
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| GHSA-4374-p667-p6c8 HTTP/2 rapid reset can cause excessive work in net/http | High Known exploited | Also affects golang.org/x/net |
| GHSA-qppj-fm5r-hxr3 HTTP/2 Stream Cancellation Attack | Medium Known exploited | Also affects golang.org/x/net |
| GO-2026-6866 Check all ancestor namespace transitions when rendering raw text in html in golang.org/x/net | Not rated yet | Also affects golang.org/x/net |
| GO-2026-6860 Avoid quadratic complexity when coalescing text nodes in html in golang.org/x/net | Not rated yet | Also affects golang.org/x/net |
| GO-2026-6617 HTTP/2 server crash due to HPACK encoder race in net/http | High | Also affects golang.org/x/net |
| GO-2026-6612 Double flow control refund on HTTP/2 server streams in net/http | Critical | Also affects golang.org/x/net |
| GO-2026-6611 Excessive CPU consumption from repeated initial window changes in net/http | High | Also affects golang.org/x/net |
| GO-2026-6610 HTTP/2 transport accepts malformed framing-related headers in net/http | High | Also affects golang.org/x/net |
Credits: Tristan Madani
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