UBUNTU-CVE-2024-43882
In the Linux kernel, the following vulnerability has been resolved: exec: Fix ToCToU between perm check and set-uid/gid usage When opening a file for exec via do_filp_open(), permission checking is done against the file's metadata at that moment, and on success, a file pointer is passed back. Much later in the execve() code path, the file metadata (specifically mode, uid, and gid) is used to determine if/how to set the uid and gid. However, those values may have changed since the permissions check, meaning the execution may gain unintended privileges. For example, if a file could change permissions from executable and not set-id: ---------x 1 root root 16048 Aug 7 13:16 target to set-id and non-executable: ---S------ 1 root root 16048 Aug 7 13:16 target it is possible to gain root privileges when execution should have been disallowed. While this race condition is rare in real-world scenarios, it has been observed (and proven exploitable) when package managers are updating the setuid bits of installed programs. Such files start with being world-executable but then are adjusted to be group-exec with a set-uid bit. For example, "chmod o-x,u+s target" makes "target" executable only by uid "root" and gid "cdrom", while also becoming setuid-root: -rwxr-xr-x 1 root cdrom 16048 Aug 7 13:16 target becomes: -rwsr-xr-- 1 root cdrom 16048 Aug 7 13:16 target But racing the chmod means users without group "cdrom" membership can get the permission to execute "target" just before the chmod, and when the chmod finishes, the exec reaches brpm_fill_uid(), and performs the setuid to root, violating the expressed authorization of "only cdrom group members can setuid to root". Re-check that we still have execute permissions in case the metadata has changed. It would be better to keep a copy from the perm-check time, but until we can do that refactoring, the least-bad option is to do a full inode_permission() call (under inode lock). It is understood that this is safe against dead-locks, but hardly optimal.
02 / AFFECTED SOFTWARE
Affected packages
11 explicit affected versions
38 explicit affected versions
52 explicit affected versions
50 explicit affected versions
6 explicit affected versions
12 explicit affected versions
19 explicit affected versions
6 explicit affected versions
61 explicit affected versions
13 explicit affected versions
47 explicit affected versions
68 explicit affected versions
57 explicit affected versions
47 explicit affected versions
10 explicit affected versions
7 explicit affected versions
13 explicit affected versions
54 explicit affected versions
191 explicit affected versions
7 explicit affected versions
53 explicit affected versions
8 explicit affected versions
95 explicit affected versions
13 explicit affected versions
66 explicit affected versions
10 explicit affected versions
35 explicit affected versions
14 explicit affected versions
18 explicit affected versions
18 explicit affected versions
15 explicit affected versions
97 explicit affected versions
64 explicit affected versions
13 explicit affected versions
97 explicit affected versions
13 explicit affected versions
4 explicit affected versions
23 explicit affected versions
102 explicit affected versions
17 explicit affected versions
1 explicit affected versions
21 explicit affected versions
16 explicit affected versions
10 explicit affected versions
52 explicit affected versions
15 explicit affected versions
7 explicit affected versions
12 explicit affected versions
45 explicit affected versions
12 explicit affected versions
14 explicit affected versions
7 explicit affected versions
85 explicit affected versions
12 explicit affected versions
100 explicit affected versions
108 explicit affected versions
12 explicit affected versions
8 explicit affected versions
96 explicit affected versions
14 explicit affected versions
8 explicit affected versions
1 explicit affected versions
10 explicit affected versions
168 explicit affected versions
37 explicit affected versions
101 explicit affected versions
13 explicit affected versions
6 explicit affected versions
10 explicit affected versions
33 explicit affected versions
1 explicit affected versions
35 explicit affected versions
26 explicit affected versions
13 explicit affected versions
9 explicit affected versions
1 explicit affected versions
29 explicit affected versions
88 explicit affected versions
13 explicit affected versions
58 explicit affected versions
7 explicit affected versions
8 explicit affected versions
1 explicit affected versions
83 explicit affected versions
56 explicit affected versions
100 explicit affected versions
18 explicit affected versions
33 explicit affected versions
23 explicit affected versions
10 explicit affected versions
1 explicit affected versions
95 explicit affected versions
11 explicit affected versions
12 explicit affected versions
118 explicit affected versions
7 explicit affected versions
12 explicit affected versions
98 explicit affected versions
2 explicit affected versions
45 explicit affected versions
39 explicit affected versions
111 explicit affected versions
55 explicit affected versions
131 explicit affected versions
10 explicit affected versions
26 explicit affected versions
15 explicit affected versions
34 explicit affected versions
1 explicit affected versions
6 explicit affected versions
16 explicit affected versions
13 explicit affected versions
15 explicit affected versions
118 explicit affected versions
58 explicit affected versions
16 explicit affected versions
58 explicit affected versions
16 explicit affected versions
46 explicit affected versions
3 explicit affected versions
72 explicit affected versions
1 explicit affected versions
2 explicit affected versions
65 explicit affected versions
51 explicit affected versions
71 explicit affected versions
13 explicit affected versions
12 explicit affected versions
44 explicit affected versions
27 explicit affected versions
30 explicit affected versions
1 explicit affected versions
1 explicit affected versions
75 explicit affected versions
9 explicit affected versions
8 explicit affected versions
19 explicit affected versions
5 explicit affected versions
8 explicit affected versions
1 explicit affected versions
10 explicit affected versions
12 explicit affected versions
13 explicit affected versions
87 explicit affected versions
13 explicit affected versions
52 explicit affected versions
7 explicit affected versions
73 explicit affected versions
50 explicit affected versions
10 explicit affected versions
14 explicit affected versions
12 explicit affected versions
87 explicit affected versions
44 explicit affected versions
16 explicit affected versions
3 explicit affected versions
13 explicit affected versions
26 explicit affected versions
44 explicit affected versions
37 explicit affected versions
16 explicit affected versions
14 explicit affected versions
38 explicit affected versions
47 explicit affected versions
9 explicit affected versions
47 explicit affected versions
11 explicit affected versions
145 explicit affected versions
7 explicit affected versions
7 explicit affected versions
55 explicit affected versions
7 explicit affected versions
28 explicit affected versions
78 explicit affected versions
59 explicit affected versions
122 explicit affected versions
101 explicit affected versions
4 explicit affected versions
1 explicit affected versions
1 explicit affected versions
53 explicit affected versions
94 explicit affected versions
13 explicit affected versions
43 explicit affected versions
53 explicit affected versions
125 explicit affected versions
145 explicit affected versions
10 explicit affected versions
8 explicit affected versions
11 explicit affected versions
14 explicit affected versions
88 explicit affected versions
4 explicit affected versions
77 explicit affected versions
11 explicit affected versions
1 explicit affected versions
48 explicit affected versions
9 explicit affected versions
03 / CONNECTIONS
Connected vulnerabilities
04 / EVIDENCE
Source records
In the Linux kernel, the following vulnerability has been resolved: exec: Fix ToCToU between perm check and set-uid/gid usage When opening a file for exec via do_filp_open(), permission checking is done against the file's metadata at that moment, and on success, a file pointer is passed back. Much later in the execve() code path, the file metadata (specifically mode, uid, and gid) is used to determine if/how to set the uid and gid. However, those values may have changed since the permissions check, meaning the execution may gain unintended privileges. For example, if a file could change permissions from executable and not set-id: ---------x 1 root root 16048 Aug 7 13:16 target to set-id and non-executable: ---S------ 1 root root 16048 Aug 7 13:16 target it is possible to gain root privileges when execution should have been disallowed. While this race condition is rare in real-world scenarios, it has been observed (and proven exploitable) when package managers are updating the setuid bits of installed programs. Such files start with being world-executable but then are adjusted to be group-exec with a set-uid bit. For example, "chmod o-x,u+s target" makes "target" executable only by uid "root" and gid "cdrom", while also becoming setuid-root: -rwxr-xr-x 1 root cdrom 16048 Aug 7 13:16 target becomes: -rwsr-xr-- 1 root cdrom 16048 Aug 7 13:16 target But racing the chmod means users without group "cdrom" membership can get the permission to execute "target" just before the chmod, and when the chmod finishes, the exec reaches brpm_fill_uid(), and performs the setuid to root, violating the expressed authorization of "only cdrom group members can setuid to root". Re-check that we still have execute permissions in case the metadata has changed. It would be better to keep a copy from the perm-check time, but until we can do that refactoring, the least-bad option is to do a full inode_permission() call (under inode lock). It is understood that this is safe against dead-locks, but hardly optimal.
05 / REFERENCES
Further evidence
- https://git.kernel.org/linus/f50733b45d865f91db90919f8311e2127ce5a0cb
- https://git.kernel.org/stable/c/15469d46ba34559bfe7e3de6659115778c624759
- https://git.kernel.org/stable/c/368f6985d46657b8b466a421dddcacd4051f7ada
- https://git.kernel.org/stable/c/90dfbba89ad4f0d9c9744ecbb1adac4aa2ff4f3e
- https://git.kernel.org/stable/c/9b424c5d4130d56312e2a3be17efb0928fec4d64
- https://git.kernel.org/stable/c/d2a2a4714d80d09b0f8eb6438ab4224690b7121e
- https://git.kernel.org/stable/c/d5c3c7e26275a2d83b894d30f7582a42853a958f
- https://git.kernel.org/stable/c/f50733b45d865f91db90919f8311e2127ce5a0cb
- https://git.kernel.org/stable/c/f6cfc6bcfd5e1cf76115b6450516ea4c99897ae1
- https://ubuntu.com/security/CVE-2024-43882
- https://ubuntu.com/security/notices/USN-7088-1
- https://ubuntu.com/security/notices/USN-7088-2
- https://ubuntu.com/security/notices/USN-7088-3
- https://ubuntu.com/security/notices/USN-7088-4
- https://ubuntu.com/security/notices/USN-7088-5
- https://ubuntu.com/security/notices/USN-7100-1
- https://ubuntu.com/security/notices/USN-7100-2
- https://ubuntu.com/security/notices/USN-7119-1
- https://ubuntu.com/security/notices/USN-7120-1
- https://ubuntu.com/security/notices/USN-7120-2
- https://ubuntu.com/security/notices/USN-7120-3
- https://ubuntu.com/security/notices/USN-7121-1
- https://ubuntu.com/security/notices/USN-7121-2
- https://ubuntu.com/security/notices/USN-7121-3
- https://ubuntu.com/security/notices/USN-7123-1
- https://ubuntu.com/security/notices/USN-7144-1
- https://ubuntu.com/security/notices/USN-7148-1
- https://ubuntu.com/security/notices/USN-7156-1
- https://ubuntu.com/security/notices/USN-7194-1
- https://www.cve.org/CVERecord?id=CVE-2024-43882