关联漏洞
标题：
OpenSSH 竞争条件问题漏洞
(CVE-2018-15473)
描述：OpenSSH（OpenBSD Secure Shell）是OpenBSD计划组的一套用于安全访问远程计算机的连接工具。该工具是SSH协议的开源实现，支持对所有的传输进行加密，可有效阻止窃听、连接劫持以及其他网络级的攻击。 OpenSSH 7.7及之前版本中存在竞争条件问题漏洞。该漏洞源于网络系统或产品在运行过程中，并发代码需要互斥地访问共享资源时，对于并发访问的处理不当。
描述
FAFAF
介绍
# PoC-CVE-2018-15473
OpenSSH through 7.7 is prone to a user enumeration vulnerability due to not delaying bailout for an invalid authenticating user until after the packet containing the request has been fully parsed, related to auth2-gss.c, auth2-hostbased.c, and auth2-pubkey.c.
CVE: CVE-2018-15473
Write up from https://www.openwall.com/lists/oss-security/2018/08/15/5
without patching the current version, a remote attacker can easily test whether a certain user exists or not (username enumeration) on a target OpenSSH server:
``` c
87 static int
88 userauth_pubkey(struct ssh *ssh)
89 {
101 if (!authctxt->valid) {
102 debug2("%s: disabled because of invalid user", __func__);
103 return 0;
104 }
105 if ((r = sshpkt_get_u8(ssh, &have_sig)) != 0 ||
106 (r = sshpkt_get_cstring(ssh, &pkalg, NULL)) != 0 ||
107 (r = sshpkt_get_string(ssh, &pkblob, &blen)) != 0)
108 fatal("%s: parse request failed: %s", __func__, ssh_err(r));
```
The attacker can try to authenticate a user with a malformed packet (for example, a truncated packet), and:
- if the user is invalid (it does not exist), then userauth_pubkey() returns immediately, and the server sends an SSH2_MSG_USERAUTH_FAILURE to the attacker;
- if the user is valid (it exists), then sshpkt_get_u8() fails, and the server calls fatal() and closes its connection to the attacker.
```
usage: ssh-check-username.py [-h] [-t HOSTNAME] [-p PORT] [-u USERNAME] [-w WORDLIST]
options:
-h, --help show this help message and exit
-t HOSTNAME Single target
-p PORT port to connect on: Default port is 22
-u USERNAME username you want to enumerate
-w WORDLIST enumerate multiple users
```
# DISCLAIMER
Please use this script responsibly and only on systems where you have permission to access. Unauthorized access to a system can lead to severe legal consequences.
文件快照
[4.0K] /data/pocs/a97dd7a2a705eae746a2d4375ebdaf35cc00b288
├── [1.5K] PoC_CVE-2018-15473.py
├── [1.9K] README.md
└── [ 24] wordlist.txt
0 directories, 3 files
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