Return to Answer

While the website may be down, the security email list continues to work apparently and they have emaied about a mitigation there on 30.04.2026 18:06 CET.

While the website may be down, the security email list continues to work apparently and they have emailed about a mitigation there in an email from 30.04.2026 18:06 CET.

sudo apt update && sudo apt install kmod
sudo rmmod algif_aead

sudo apt update && sudo apt install --only-upgrade kmod
sudo rmmod algif_aead

~$ sudo apt update && sudo apt upgrade kmod

I've not been able to verify what happens without a reboot or before installing that update yet, but after installation the exploit no longer works on my test server:

~$ python3 copy_fail_exp.py                         
Traceback (most recent call last):                                             
  File "/tmp/copy_fail_exp.py", line 9, in <module>                            
    while i<len(e):c(f,i,e[i:i+4]);i+=4                                        
                   ^^^^^^^^^^^^^^^                                             
  File "/tmp/copy_fail_exp.py", line 5, in c                                   
    a=s.socket(38,5,0);a.bind(("aead","authencesn(hmac(sha256),cbc(aes))"));h=2
79;v=a.setsockopt;v(h,1,d('0800010000000010'+'0'*64));v(h,5,None,4);u,_=a.accep
t();o=t+4;i=d('00');u.sendmsg([b"A"*4+c],[(h,3,i*4),(h,2,b'\x10'+i*19),(h,4,b'\
x08'+i*3),],32768);r,w=g.pipe();n=g.splice;n(f,w,o,offset_src=0);n(r,u.fileno()
,o)                                                                            
                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^    
FileNotFoundError: [Errno 2] No such file or directory

sudo apt update && sudo apt install kmod
sudo rmmod algif_aead

The mitigation works effectively and without a reboot (given that the module wasn't loaded at all or rmmod was used like suggested above), though a reboot is probably recommended:

wget https://github.com/theori-io/copy-fail-CVE-2026-31431/raw/main/copy_fail_exp.py -O /tmp/copy_fail_exp.py
python3 /tmp/copy_fail_exp.py

Result:

Traceback (most recent call last):                                             
  File "/tmp/copy_fail_exp.py", line 9, in <module>                            
    while i<len(e):c(f,i,e[i:i+4]);i+=4                                        
                   ^^^^^^^^^^^^^^^                                             
  File "/tmp/copy_fail_exp.py", line 5, in c                                   
    a=s.socket(38,5,0);a.bind(("aead","authencesn(hmac(sha256),cbc(aes))"));h=2
79;v=a.setsockopt;v(h,1,d('0800010000000010'+'0'*64));v(h,5,None,4);u,_=a.accep
t();o=t+4;i=d('00');u.sendmsg([b"A"*4+c],[(h,3,i*4),(h,2,b'\x10'+i*19),(h,4,b'\
x08'+i*3),],32768);r,w=g.pipe();n=g.splice;n(f,w,o,offset_src=0);n(r,u.fileno()
,o)                                                                            
                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^    
FileNotFoundError: [Errno 2] No such file or directory