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hackeroneAaron_costelloH1:789034
HistoryFeb 04, 2020 - 9:58 p.m.

Internet Bug Bounty: Buffer Overflow in ext_lm_group_acl helper

2020-02-0421:58:53
aaron_costello
hackerone.com
26

7.5 High

CVSS3

Attack Vector

NETWORK

Attack Complexity

LOW

Privileges Required

NONE

User Interaction

NONE

Scope

UNCHANGED

Confidentiality Impact

NONE

Integrity Impact

NONE

Availability Impact

HIGH

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

5 Medium

CVSS2

Access Vector

NETWORK

Access Complexity

LOW

Authentication

NONE

Confidentiality Impact

NONE

Integrity Impact

NONE

Availability Impact

PARTIAL

AV:N/AC:L/Au:N/C:N/I:N/A:P

0.004 Low

EPSS

Percentile

74.6%

Summary

Due to incorrect buffer management ext_lm_group_acl is vulnerable to a denial of service attack when processing NTLM Authentication credentials. This problem is limited to installations using the
ext_lm_group_acl binary.

Affected Versions

Squid 2.x -> 2.7.STABLE9
Squid 3.x -> 3.5.28
Squid 4.x -> 4.9

Severity

Due to incorrect input validation the NTLM authentication credentials parser in ext_lm_group_acl may write to memory outside the credentials buffer. On systems with memory access protections this can result in the helper process being terminated unexpectedly. Resulting in the Squid process also terminating and a denial of service for all clients using the proxy.

Supporting Material/References:

Advisory : http://www.squid-cache.org/Advisories/SQUID-2020_3.txt

Remediation

An official patch is available from the Squid archives for both Squid 3.5 and Squid 4.

Timeline

2019-11-11 : I reported the issue
2019-11-18 : I made a PR on GitHub with a fix
2019-11-22 : Fix was merged

Impact

See β€˜Severity’ section of report.

7.5 High

CVSS3

Attack Vector

NETWORK

Attack Complexity

LOW

Privileges Required

NONE

User Interaction

NONE

Scope

UNCHANGED

Confidentiality Impact

NONE

Integrity Impact

NONE

Availability Impact

HIGH

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

5 Medium

CVSS2

Access Vector

NETWORK

Access Complexity

LOW

Authentication

NONE

Confidentiality Impact

NONE

Integrity Impact

NONE

Availability Impact

PARTIAL

AV:N/AC:L/Au:N/C:N/I:N/A:P

0.004 Low

EPSS

Percentile

74.6%