The vulnerable system 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). An example of a network attack is an attacker causing a denial of service by sending a specially crafted TCP packet across a wide area network (e.g., CVE-2004-0230).
Attack Complexity
Low
AC
The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Privileges Required
Low
PR
The attacker requires privileges that provide basic capabilities that are typically limited to settings and resources owned by a single low-privileged user. Alternatively, an attacker with Low privileges has the ability to access only non-sensitive resources.
User Interaction
None
UI
The vulnerable system can be exploited without interaction from any human user, other than the attacker. Examples include: a remote attacker is able to send packets to a target system a locally authenticated attacker executes code to elevate privileges
Scope
Unchanged
S
An exploited vulnerability can only affect resources managed by the same security authority. In the case of a vulnerability in a virtualized environment, an exploited vulnerability in one guest instance would not affect neighboring guest instances.
Confidentiality
Low
C
There is some impact on confidentiality, but the attacker either does not gain control of any data, or the information obtained does not have a significant impact on the system or its operations.
Integrity
None
I
There is no impact on the integrity of the system; the attacker does not gain the ability to modify any files or information on the target system.
Availability
None
A
There is no impact on the availability of the system; the attacker does not have the ability to disrupt access to or use of the system.
Below is a copy: CUPS Weak Session Cookie Generation
CUPS: session cookies are generated with srandom(time(NULL)) and random() on Linux
CVE-2018-4700
CUPS generates session cookies as follows in cgi_set_sid():
============
if ((remote_addr = getenv("REMOTE_ADDR")) == NULL)
remote_addr = "REMOTE_ADDR";
if ((server_name = getenv("SERVER_NAME")) == NULL)
server_name = "SERVER_NAME";
if ((server_port = getenv("SERVER_PORT")) == NULL)
server_port = "SERVER_PORT";
CUPS_SRAND(time(NULL));
snprintf(buffer, sizeof(buffer), "%s:%s:%s:%02X%02X%02X%02X%02X%02X%02X%02X",
remote_addr, server_name, server_port,
(unsigned)CUPS_RAND() & 255, (unsigned)CUPS_RAND() & 255,
(unsigned)CUPS_RAND() & 255, (unsigned)CUPS_RAND() & 255,
(unsigned)CUPS_RAND() & 255, (unsigned)CUPS_RAND() & 255,
(unsigned)CUPS_RAND() & 255, (unsigned)CUPS_RAND() & 255);
cupsHashData("md5", (unsigned char *)buffer, strlen(buffer), sum, sizeof(sum));
cgiSetCookie(CUPS_SID, cupsHashString(sum, sizeof(sum), sid, sizeof(sid)), "/", NULL, 0, 0);
============
Note the CUPS_SRAND(time(NULL)).
CUPS_SRAND() and CUPS_RAND() have four possible definitions, depending on the environment:
============
#ifdef HAVE_ARC4RANDOM
# define CUPS_RAND() arc4random()
# define CUPS_SRAND(v)
#elif defined(HAVE_RANDOM)
# define CUPS_RAND() random()
# define CUPS_SRAND(v) srandom(v)
#elif defined(HAVE_LRAND48)
# define CUPS_RAND() lrand48()
# define CUPS_SRAND(v) srand48(v)
#else
# define CUPS_RAND() rand()
# define CUPS_SRAND(v) srand(v)
#endif /* HAVE_ARC4RANDOM */
============
On a typical Linux system, HAVE_ARC4RANDOM is not defined, but HAVE_RANDOM is defined; so CUPS_RAND() is random(), and CUPS_SRAND() is srandom().
This means that the session cookie is extremely predictable, effectively breaking the CSRF protection of the CUPS web interface.
Luckily, this isn't very useful unless the user has already authenticated to CUPS; and because CUPS uses HTTP basic auth for authentication, an attacker can't forcibly sign the user in (e.g. Chrome forbids it completely, Firefox shows a confirmation prompt).
This bug is subject to a 90 day disclosure deadline. After 90 days elapse
or a patch has been made broadly available (whichever is earlier), the bug
report will become visible to the public.
Found by: jannh
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