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CAPEC-67: String Format Overflow in syslog()

Attack Pattern ID: 67
Abstraction: Detailed
Status: Draft
Presentation Filter:
+ Description
This attack targets applications and software that uses the syslog() function insecurely. If an application does not explicitely use a format string parameter in a call to syslog(), user input can be placed in the format string parameter leading to a format string injection attack. Adversaries can then inject malicious format string commands into the function call leading to a buffer overflow. There are many reported software vulnerabilities with the root cause being a misuse of the syslog() function.
+ Likelihood Of Attack

High

+ Typical Severity

Very High

+ Relationships
Section HelpThis table shows the other attack patterns and high level categories that are related to this attack pattern. These relationships are defined as ChildOf and ParentOf, and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as CanFollow, PeerOf, and CanAlsoBe are defined to show similar attack patterns that the user may want to explore.
NatureTypeIDName
ChildOfStandard Attack PatternStandard Attack Pattern - A standard level attack pattern in CAPEC is focused on a specific methodology or technique used in an attack. It is often seen as a singular piece of a fully executed attack. A standard attack pattern is meant to provide sufficient details to understand the specific technique and how it attempts to accomplish a desired goal. A standard level attack pattern is a specific type of a more abstract meta level attack pattern.100Overflow Buffers
ChildOfStandard Attack PatternStandard Attack Pattern - A standard level attack pattern in CAPEC is focused on a specific methodology or technique used in an attack. It is often seen as a singular piece of a fully executed attack. A standard attack pattern is meant to provide sufficient details to understand the specific technique and how it attempts to accomplish a desired goal. A standard level attack pattern is a specific type of a more abstract meta level attack pattern.135Format String Injection
CanFollowStandard Attack PatternStandard Attack Pattern - A standard level attack pattern in CAPEC is focused on a specific methodology or technique used in an attack. It is often seen as a singular piece of a fully executed attack. A standard attack pattern is meant to provide sufficient details to understand the specific technique and how it attempts to accomplish a desired goal. A standard level attack pattern is a specific type of a more abstract meta level attack pattern.69Target Programs with Elevated Privileges
Section HelpThis table shows the views that this attack pattern belongs to and top level categories within that view.
+ Execution Flow
Explore
  1. Identify target application: The adversary identifies a target application or program to perform the buffer overflow on. In this attack, adversaries look for applications that use syslog() incorrectly.

Experiment
  1. Find injection vector: The adversary identifies an injection vector to deliver the excessive content to the targeted application's buffer. For each user-controllable input that the adversary suspects is vulnerable to format string injection, attempt to inject formatting characters such as %n, %s, etc.. The goal is to manipulate the string creation using these formatting characters.

    Techniques
    Inject probe payload which contains formatting characters (%s, %d, %n, etc.) through input parameters.
  2. Craft overflow content: The adversary crafts the content to be injected. If the intent is to simply cause the software to crash, the content need only consist of an excessive quantity of random data. If the intent is to leverage the overflow for execution of arbitrary code, the adversary will craft a set of content that not only overflows the targeted buffer but does so in such a way that the overwritten return address is replaced with one of the adversaries' choosing which points to code injected by the adversary.

    Techniques
    The formatting characters %s and %d are useful for observing memory and trying to print memory addresses. If an adversary has access to the log being written to they can observer this output and use it to help craft their attack.
    The formatting character %n is useful for adding extra data onto the buffer.
Exploit
  1. Overflow the buffer: Using the injection vector, the adversary supplies the program with the crafted format string injection, causing a buffer.

+ Prerequisites
The Syslog function is used without specifying a format string argument, allowing user input to be placed direct into the function call as a format string.
+ Consequences
Section HelpThis table specifies different individual consequences associated with the attack pattern. The Scope identifies the security property that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in their attack. The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. For example, there may be high likelihood that a pattern will be used to achieve a certain impact, but a low likelihood that it will be exploited to achieve a different impact.
ScopeImpactLikelihood
Confidentiality
Integrity
Availability
Execute Unauthorized Commands
Availability
Unreliable Execution
Confidentiality
Access Control
Authorization
Gain Privileges
Integrity
Modify Data
+ Mitigations

The code should be reviewed for misuse of the Syslog function call. Manual or automated code review can be used. The reviewer needs to ensure that all format string functions are passed a static string which cannot be controlled by the user and that the proper number of arguments are always sent to that function as well. If at all possible, do not use the %n operator in format strings. The following code shows a correct usage of Syslog():

syslog(LOG_ERR, "%s", cmdBuf);

The following code shows a vulnerable usage of Syslog():

syslog(LOG_ERR, cmdBuf);
// the buffer cmdBuff is taking user supplied data.
+ Example Instances
Format string vulnerability in TraceEvent function for ntop before 2.1 allows remote attackers to execute arbitrary code by causing format strings to be injected into calls to the syslog function, via (1) an HTTP GET request, (2) a user name in HTTP authentication, or (3) a password in HTTP authentication. See also: CVE-2002-0412
+ Taxonomy Mappings
Relevant to the WASC taxonomy mapping
Entry IDEntry Name
06Format String
+ References
[REF-1] G. Hoglund and G. McGraw. "Exploiting Software: How to Break Code". Addison-Wesley. 2004-02.
[REF-503] scut and team teso. "Exploiting Format String Vulnerabilities". <http://doc.bughunter.net/format-string/exploit-fs.html>.
[REF-504] Halvar Flake. "Auditing binaries for security vulnerabilities". <http://www.blackhat.com/presentations/bh-europe-00/HalvarFlake/HalvarFlake.ppt>.
[REF-505] "Fortify Taxonomy of Vulnerabilities". Fortify Software. <https://vulncat.hpefod.com/en>.
[REF-506] "Syslog man page". <http://www.rt.com/man/syslog.3.html>.
+ Content History
Submissions
Submission DateSubmitterOrganization
2014-06-23CAPEC Content TeamThe MITRE Corporation
Modifications
Modification DateModifierOrganization
2017-01-09CAPEC Content TeamThe MITRE Corporation
Updated Related_Attack_Patterns
2018-07-31CAPEC Content TeamThe MITRE Corporation
Updated References
2020-07-30CAPEC Content TeamThe MITRE Corporation
Updated Execution_Flow
2020-12-17CAPEC Content TeamThe MITRE Corporation
Updated Taxonomy_Mappings
2021-10-21CAPEC Content TeamThe MITRE Corporation
Updated Description, Execution_Flow, Prerequisites, Related_Attack_Patterns
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Page Last Updated or Reviewed: October 21, 2021