Non-linear Parsing Vulnerability in golang.org/x/net/html

Published Date: December 19, 2024

Package Affected Versions Patched Versions Severity
📦 golang.org/x/net (Go) < 0.33.0 0.33.0 High

Description

Vulnerability Overview


The golang.org/x/net/html package contains a vulnerability in its parsing logic. When given specially crafted input, the Parse functions process the content in a way that is non-linear relative to the input’s length. This means the parsing time increases disproportionately as the input size grows. An attacker could exploit this to cause extremely slow parsing, effectively leading to a denial of service (DoS).

 

Potential Impact


Applications relying on the golang.org/x/net/html package are at risk of DoS if they process untrusted input using the vulnerable Parse functions. Attackers can exploit this by submitting intentionally malformed or excessively large input, tying up resources and rendering the application unresponsive.

Patches & Workarounds

Recommendation: How to Fix


Upgrade to a Patched Version



  • Update the golang.org/x/net package to version 0.33.0 or later:


go get golang.org/x/net@v0.33.0


  • Rebuild your application after updating the dependency.


Temporary Workaround


If upgrading immediately is not an option, consider the following mitigations:

  1. Input Validation: Validate and limit input size before parsing. Reject excessively large or suspicious inputs.

  2. Rate Limiting: Implement rate limiting for requests or inputs being parsed to prevent abuse.

  3. Timeouts: Use a timeout mechanism during parsing to abort processing for overly long tasks.






Example Fix


Here’s an example of restricting input size before parsing:

package main


import (

“bytes”

“golang.org/x/net/html”

“io”

)


const MaxInputSize = 10 * 1024 // 10 KB limit


func safeParse(input io.Reader) (*html.Node, error) {

limitedInput := io.LimitReader(input, MaxInputSize)

return html.Parse(limitedInput)

}

This code ensures that any input exceeding 10 KB is ignored, reducing the risk of DoS.

References

https://nvd.nist.gov/vuln/detail/CVE-2024-45338

https://go.dev/cl/637536

https://go.dev/issue/70906

https://groups.google.com/g/golang-announce/c/wSCRmFnNmPA/m/Lvcd0mRMAwAJ

https://pkg.go.dev/vuln/GO-2024-3333
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