Language: Go
Label: vulnerable
CWE: CWE-77 \u2014 Improper Neutralization of Special Elements used in a Command ('Command Injection')
The product constructs all or part of a command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended command when it is sent to a downstream component.

Code:
func (v *SnapshotJob) do(ffmpegPath, inputUrl string) (err error) {
	outputPicDir := path.Join(StaticDir, v.App)
	if err = os.MkdirAll(outputPicDir, 0777); err != nil {
		log.Println(fmt.Sprintf("create snapshot image dir:%v failed, err is %v", outputPicDir, err))
		return
	}

	normalPicPath := path.Join(outputPicDir, fmt.Sprintf("%v", v.Stream)+"-%03d.png")
	bestPng := path.Join(outputPicDir, fmt.Sprintf("%v-best.png", v.Stream))

	param := fmt.Sprintf("%v -i %v -vf fps=1 -vcodec png -f image2 -an -y -vframes %v -y %v", ffmpegPath, inputUrl, v.vframes, normalPicPath)
	log.Println(fmt.Sprintf("start snapshot, cmd param=%v", param))
	timeoutCtx, _ := context.WithTimeout(v.cancelCtx, v.timeout)
	cmd := exec.CommandContext(timeoutCtx, "/bin/bash", "-c", param)
	if err = cmd.Run(); err != nil {
		log.Println(fmt.Sprintf("run snapshot %v cmd failed, err is %v", v.Tag(), err))
		return
	}

	bestFileSize := int64(0)
	for i := 1; i <= v.vframes; i++ {
		pic := path.Join(outputPicDir, fmt.Sprintf("%v-%03d.png", v.Stream, i))
		fi, err := os.Stat(pic)
		if err != nil {
			log.Println(fmt.Sprintf("stat pic:%v failed, err is %v", pic, err))
			continue
		}
		if bestFileSize == 0 {
			bestFileSize = fi.Size()
		} else if fi.Size() > bestFileSize {
			os.Remove(bestPng)
			os.Symlink(pic, bestPng)
			bestFileSize = fi.Size()
		}
	}
	log.Println(fmt.Sprintf("%v the best thumbnail is %v", v.Tag(), bestPng))
	return
}