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Home > CWE List > CWE-93: Improper Neutralization of CRLF Sequences ('CRLF Injection') (4.17)  
ID

CWE-93: Improper Neutralization of CRLF Sequences ('CRLF Injection')

Weakness ID: 93
Vulnerability Mapping: ALLOWED This CWE ID may be used to map to real-world vulnerabilities
Abstraction: Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.
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+ Description
The product uses CRLF (carriage return line feeds) as a special element, e.g. to separate lines or records, but it does not neutralize or incorrectly neutralizes CRLF sequences from inputs. Diagram for CWE-93
+ Common Consequences
Section HelpThis table specifies different individual consequences associated with the weakness. The Scope identifies the application security area that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in exploiting this weakness. 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 weakness will be exploited to achieve a certain impact, but a low likelihood that it will be exploited to achieve a different impact.
Impact Details

Modify Application Data

Scope: Integrity

+ Potential Mitigations
Phase(s) Mitigation

Implementation
Avoid using CRLF as a special sequence.

Implementation
Appropriately filter or quote CRLF sequences in user-controlled input.
+ Relationships
Section Help This table shows the weaknesses and high level categories that are related to this weakness. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user may want to explore.
+ Relevant to the view "Research Concepts" (View-1000)
Nature Type ID Name
ChildOf Class Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource. 74 Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')
ParentOf Variant Variant - a weakness that is linked to a certain type of product, typically involving a specific language or technology. More specific than a Base weakness. Variant level weaknesses typically describe issues in terms of 3 to 5 of the following dimensions: behavior, property, technology, language, and resource. 113 Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting')
CanPrecede Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource. 117 Improper Output Neutralization for Logs
+ Relevant to the view "Software Development" (View-699)
Nature Type ID Name
MemberOf Category Category - a CWE entry that contains a set of other entries that share a common characteristic. 137 Data Neutralization Issues
+ Relevant to the view "Architectural Concepts" (View-1008)
Nature Type ID Name
MemberOf Category Category - a CWE entry that contains a set of other entries that share a common characteristic. 1019 Validate Inputs
+ Modes Of Introduction
Section HelpThe different Modes of Introduction provide information about how and when this weakness may be introduced. The Phase identifies a point in the life cycle at which introduction may occur, while the Note provides a typical scenario related to introduction during the given phase.
Phase Note
Implementation REALIZATION: This weakness is caused during implementation of an architectural security tactic.
+ Applicable Platforms
Section HelpThis listing shows possible areas for which the given weakness could appear. These may be for specific named Languages, Operating Systems, Architectures, Paradigms, Technologies, or a class of such platforms. The platform is listed along with how frequently the given weakness appears for that instance.
Languages

Class: Not Language-Specific (Undetermined Prevalence)

+ Demonstrative Examples

Example 1


The following code segment reads the name of the author of a weblog entry, author, from an HTTP request and sets it in a cookie header of an HTTP response.

(bad code)
Example Language: Java 
String author = request.getParameter(AUTHOR_PARAM);
...
Cookie cookie = new Cookie("author", author);
cookie.setMaxAge(cookieExpiration);
response.addCookie(cookie);

Assuming a string consisting of standard alpha-numeric characters, such as "Jane Smith", is submitted in the request the HTTP response including this cookie might take the following form:

(result)
 
HTTP/1.1 200 OK
...
Set-Cookie: author=Jane Smith
...

However, because the value of the cookie is composed of unvalidated user input, the response will only maintain this form if the value submitted for AUTHOR_PARAM does not contain any CR and LF characters. If an attacker submits a malicious string, such as

(attack code)
 
Wiley Hacker\r\nHTTP/1.1 200 OK\r\n

then the HTTP response would be split into two responses of the following form:

(result)
 
HTTP/1.1 200 OK
...
Set-Cookie: author=Wiley Hacker
HTTP/1.1 200 OK
...

The second response is completely controlled by the attacker and can be constructed with any header and body content desired. The ability to construct arbitrary HTTP responses permits a variety of resulting attacks, including:

  • cross-user defacement
  • web and browser cache poisoning
  • cross-site scripting
  • page hijacking



Example 2


If user input data that eventually makes it to a log message isn't checked for CRLF characters, it may be possible for an attacker to forge entries in a log file.

(bad code)
Example Language: Java 
logger.info("User's street address: " + request.getParameter("streetAddress"));


+ Selected Observed Examples

Note: this is a curated list of examples for users to understand the variety of ways in which this weakness can be introduced. It is not a complete list of all CVEs that are related to this CWE entry.

Reference Description
CRLF injection enables spam proxy (add mail headers) using email address or name.
CRLF injection in API function arguments modify headers for outgoing requests.
Spoofed entries in web server log file via carriage returns
Chain: inject fake log entries with fake timestamps using CRLF injection
Chain: Application accepts CRLF in an object ID, allowing HTTP response splitting.
Chain: HTTP response splitting via CRLF in parameter related to URL.
+ Weakness Ordinalities
Ordinality Description
Primary
(where the weakness exists independent of other weaknesses)
+ Detection Methods
Method Details

Automated Static Analysis
Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)

Effectiveness: High
+ Memberships
Section HelpThis MemberOf Relationships table shows additional CWE Categories and Views that reference this weakness as a member. This information is often useful in understanding where a weakness fits within the context of external information sources.
Nature Type ID Name
MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 713 OWASP Top Ten 2007 Category A2 - Injection Flaws
MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 990 SFP Secondary Cluster: Tainted Input to Command
MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 1347 OWASP Top Ten 2021 Category A03:2021 - Injection
MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 1409 Comprehensive Categorization: Injection
+ Vulnerability Mapping Notes
Usage ALLOWED
(this CWE ID may be used to map to real-world vulnerabilities)
Reason Acceptable-Use

Rationale

This CWE entry is at the Base level of abstraction, which is a preferred level of abstraction for mapping to the root causes of vulnerabilities.

Comments

Carefully read both the name and description to ensure that this mapping is an appropriate fit. Do not try to 'force' a mapping to a lower-level Base/Variant simply to comply with this preferred level of abstraction.
+ Taxonomy Mappings
Mapped Taxonomy Name Node ID Fit Mapped Node Name
PLOVER CRLF Injection
OWASP Top Ten 2007 A2 CWE More Specific Injection Flaws
WASC 24 HTTP Request Splitting
Software Fault Patterns SFP24 Tainted input to command
+ References
[REF-928] Ulf Harnhammar. "CRLF Injection". Bugtraq. 2002-05-07.
<http://marc.info/?l=bugtraq&m=102088154213630&w=2>.
[REF-1456] Imperva. "CRLF Injection".
<https://www.imperva.com/learn/application-security/crlf-injection//>. (URL validated: 2025-02-21)
[REF-1457] R00tendo. "CRLF injection". 2024-02-25.
<https://medium.com/@R00tendo/crlf-injection-ae26521c5e4c>. (URL validated: 2025-02-21)
+ Content History
+ Submissions
Submission Date Submitter Organization
2006-07-19
(CWE Draft 3, 2006-07-19) 		PLOVER
+ Modifications
Modification Date Modifier Organization
2025-04-03
(CWE 4.17, 2025-04-03) 		CWE Content Team MITRE
updated Diagram, References
2024-11-19
(CWE 4.16, 2024-11-19) 		CWE Content Team MITRE
updated Demonstrative_Examples
2023-06-29 CWE Content Team MITRE
updated Mapping_Notes
2023-04-27 CWE Content Team MITRE
updated Detection_Factors, Relationships, Time_of_Introduction
2023-01-31 CWE Content Team MITRE
updated Description
2022-04-28 CWE Content Team MITRE
updated Research_Gaps
2021-10-28 CWE Content Team MITRE
updated Relationships
2020-02-24 CWE Content Team MITRE
updated Relationships
2019-06-20 CWE Content Team MITRE
updated Relationships
2017-11-08 CWE Content Team MITRE
updated Applicable_Platforms, Causal_Nature, Likelihood_of_Exploit, Modes_of_Introduction, References, Relationships
2015-12-07 CWE Content Team MITRE
updated Relationships
2014-07-30 CWE Content Team MITRE
updated Relationships, Taxonomy_Mappings
2012-10-30 CWE Content Team MITRE
updated Potential_Mitigations
2012-05-11 CWE Content Team MITRE
updated Relationships
2011-06-01 CWE Content Team MITRE
updated Common_Consequences
2011-03-29 CWE Content Team MITRE
updated Description
2010-06-21 CWE Content Team MITRE
updated Description, Name
2010-04-05 CWE Content Team MITRE
updated Related_Attack_Patterns
2010-02-16 CWE Content Team MITRE
updated Related_Attack_Patterns, Taxonomy_Mappings
2009-12-28 CWE Content Team MITRE
updated Likelihood_of_Exploit
2009-10-29 CWE Content Team MITRE
updated Other_Notes
2009-05-27 CWE Content Team MITRE
updated Name
2009-03-10 CWE Content Team MITRE
updated References
2008-09-08 CWE Content Team MITRE
updated Relationships, Other_Notes, Taxonomy_Mappings, Weakness_Ordinalities
2008-07-01 Eric Dalci Cigital
updated Time_of_Introduction
2008-07-01 Sean Eidemiller Cigital
added/updated demonstrative examples
+ Previous Entry Names
Change Date Previous Entry Name
2008-04-11 CRLF Injection
2009-05-27 Failure to Sanitize CRLF Sequences (aka 'CRLF Injection')
2010-06-21 Failure to Sanitize CRLF Sequences ('CRLF Injection')
Page Last Updated: April 03, 2025
 

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