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6 <title>Samba - Security Announcement Archive</title>
11 <H2>CVE-2020-27840.html:</H2>
15 ===========================================================
16 == Subject: Heap corruption via crafted DN strings
18 == CVE ID#: CVE-2020-27840
20 == Versions: All Samba versions since Samba 4.0.0
22 == Summary: An anonymous attacker can crash the Samba AD DC
23 == LDAP server by sending easily crafted DNs as
24 == part of a bind request. More serious heap corruption
25 == is likely also possible.
26 ===========================================================
32 A DN may be represented in string form with arbitrary amounts of space
33 around the component values. These spaces are supposed to be ignored,
34 but invalid DNs strings with spaces may instead cause a zero byte to
35 be written into out-of-bounds memory.
37 An LDAP bind request can send a string DN as a username. This DN is
38 necessarily parsed before the password is checked, so an attacker
39 without real credentials can anonymously trigger this bug.
41 The location of zero byte is a negative offset relative to the
42 location of a dynamically allocated heap buffer; the exact offset
43 depends on the DN string. While it is possible for an attacker to
44 cause non-fatal data corruption, usefully targeting this is likely to
45 be difficult and the most likely outcome is a crash.
47 The affected parsing routine is widely used. LDAP bind is not the only
48 way to trigger the bug remotely, though it appears to be the only
49 unauthenticated method.
51 For technical details of the vulnerability, see the patch and
52 the bug at https://bugzilla.samba.org/show_bug.cgi?id=14595.
58 Patches addressing both these issues have been posted to:
60 https://www.samba.org/samba/security/
62 Additionally, Samba 4.14.2 (4.14.1), 4.13.7 (4.13.6) and 4.12.14 (4.12.13) have
63 been issued as security releases to correct the defect. Samba administrators
64 are advised to upgrade to these releases or apply the patch as soon as possible.
70 CVSSv3.1: AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H (7.5)
72 =========================
73 Workaround and mitigation
74 =========================
82 Found and fixed by Douglas Bagnall of Catalyst and the Samba Team,
85 Advisory written by Douglas Bagnall.
87 ==========================================================
88 == Our Code, Our Bugs, Our Responsibility.
90 ==========================================================