CWE

CWE-186 – Overly Restrictive Regular Expression

May 26, 2022 rocco

Read Time:1 Minute, 14 Second

Description

A regular expression is overly restrictive, which prevents dangerous values from being detected.

This weakness is not about regular expression complexity. Rather, it is about a regular expression that does not match all values that are intended. Consider the use of a regexp to identify acceptable values or to spot unwanted terms. An overly restrictive regexp misses some potentially security-relevant values leading to either false positives *or* false negatives, depending on how the regexp is being used within the code. Consider the expression /[0-8]/ where the intention was /[0-9]/. This expression is not “complex” but the value “9” is not matched when maybe the programmer planned to check for it.

Modes of Introduction:

– Implementation

Related Weaknesses

CWE-185
CWE-184
CWE-183

Consequences

Access Control: Bypass Protection Mechanism

Potential Mitigations

Phase: Implementation

Description:

Regular expressions can become error prone when defining a complex language even for those experienced in writing grammars. Determine if several smaller regular expressions simplify one large regular expression. Also, subject your regular expression to thorough testing techniques such as equivalence partitioning, boundary value analysis, and robustness. After testing and a reasonable confidence level is achieved, a regular expression may not be foolproof. If an exploit is allowed to slip through, then record the exploit and refactor your regular expression.

CVE References

CVE-2005-1604
- MIE. “.php.ns” bypasses “.php$” regexp but is still parsed as PHP by Apache. (manipulates an equivalence property under Apache)

CWE

CWE-185 – Incorrect Regular Expression

May 26, 2022 rocco

Read Time:1 Minute, 49 Second

Description

The software specifies a regular expression in a way that causes data to be improperly matched or compared.

When the regular expression is used in protection mechanisms such as filtering or validation, this may allow an attacker to bypass the intended restrictions on the incoming data.

Modes of Introduction:

– Implementation

Related Weaknesses

CWE-697
CWE-187
CWE-182

Consequences

Other: Unexpected State, Varies by Context

When the regular expression is not correctly specified, data might have a different format or type than the rest of the program expects, producing resultant weaknesses or errors.

Access Control: Bypass Protection Mechanism

In PHP, regular expression checks can sometimes be bypassed with a null byte, leading to any number of weaknesses.

Potential Mitigations

Phase: Architecture and Design

Description:

Regular expressions can become error prone when defining a complex language even for those experienced in writing grammars. Determine if several smaller regular expressions simplify one large regular expression. Also, subject the regular expression to thorough testing techniques such as equivalence partitioning, boundary value analysis, and robustness. After testing and a reasonable confidence level is achieved, a regular expression may not be foolproof. If an exploit is allowed to slip through, then record the exploit and refactor the regular expression.

CVE References

CVE-2002-2109
- Regexp isn’t “anchored” to the beginning or end, which allows spoofed values that have trusted values as substrings.

CVE-2005-1949
- Regexp for IP address isn’t anchored at the end, allowing appending of shell metacharacters.

CVE-2001-1072
- Bypass access restrictions via multiple leading slash, which causes a regular expression to fail.

CVE-2000-0115
- Local user DoS via invalid regular expressions.

CVE-2002-1527
- chain: Malformed input generates a regular expression error that leads to information exposure.

CVE-2005-1061
- Certain strings are later used in a regexp, leading to a resultant crash.

CVE-2005-2169
- MFV. Regular expression intended to protect against directory traversal reduces “…/…//” to “../”.

CVE-2005-0603
- Malformed regexp syntax leads to information exposure in error message.

CVE-2005-1820
- Code injection due to improper quoting of regular expression.

CVE-2005-3153
- Null byte bypasses PHP regexp check.

CVE-2005-4155
- Null byte bypasses PHP regexp check.

CWE

CWE-184 – Incomplete List of Disallowed Inputs

May 26, 2022 rocco

Read Time:2 Minute, 27 Second

Description

The product implements a protection mechanism that relies on a list of inputs (or properties of inputs) that are not allowed by policy or otherwise require other action to neutralize before additional processing takes place, but the list is incomplete, leading to resultant weaknesses.

Developers often try to protect their products against malicious input by performing tests against inputs that are known to be bad, such as special characters that can invoke new commands. However, such lists often only account for the most well-known bad inputs. Attackers may be able to find other malicious inputs that were not expected by the developer, allowing them to bypass the intended protection mechanism.

Modes of Introduction:

– Implementation

Related Weaknesses

CWE-693
CWE-1023
CWE-79
CWE-78
CWE-434
CWE-98

Consequences

Access Control: Bypass Protection Mechanism

Potential Mitigations

Phase: Implementation

Description:

Do not rely exclusively on detecting disallowed inputs. There are too many variants to encode a character, especially when different environments are used, so there is a high likelihood of missing some variants. Only use detection of disallowed inputs as a mechanism for detecting suspicious activity. Ensure that you are using other protection mechanisms that only identify “good” input – such as lists of allowed inputs – and ensure that you are properly encoding your outputs.

CVE References

CVE-2008-2309
- product uses a denylist to identify potentially dangerous content, allowing attacker to bypass a warning

CVE-2005-2782
- PHP remote file inclusion in web application that filters “http” and “https” URLs, but not “ftp”.

CVE-2004-0542
- Programming language does not filter certain shell metacharacters in Windows environment.

CVE-2004-0595
- XSS filter doesn’t filter null characters before looking for dangerous tags, which are ignored by web browsers. MIE and validate-before-cleanse.

CVE-2005-3287
- Web-based mail product doesn’t restrict dangerous extensions such as ASPX on a web server, even though others are prohibited.

CVE-2004-2351
- Resultant XSS when only

Read Time:45 Second

Description

The product implements a protection mechanism that relies on a list of inputs (or properties of inputs) that are explicitly allowed by policy because the inputs are assumed to be safe, but the list is too permissive – that is, it allows an input that is unsafe, leading to resultant weaknesses.

Modes of Introduction:

– Implementation

Related Weaknesses

CWE-697
CWE-434

Consequences

Access Control: Bypass Protection Mechanism

Potential Mitigations

CVE References

CVE-2019-12799
- chain: bypass of untrusted deserialization issue (CWE-502) by using an assumed-trusted class (CWE-183)

CVE-2019-10458
- sandbox bypass using a method that is on an allowlist

CVE-2017-1000095
- sandbox bypass using unsafe methods that are on an allowlist

CVE-2019-10458
- CI/CD pipeline feature has unsafe elements in allowlist, allowing bypass of script restrictions

CVE-2017-1000095
- Default allowlist includes unsafe methods, allowing bypass of sandbox

CWE

CWE-182 – Collapse of Data into Unsafe Value

May 26, 2022 rocco

Read Time:1 Minute, 16 Second

Description

The software filters data in a way that causes it to be reduced or “collapsed” into an unsafe value that violates an expected security property.

Modes of Introduction:

– Implementation

Related Weaknesses

CWE-693
CWE-33
CWE-34
CWE-35

Consequences

Access Control: Bypass Protection Mechanism

Potential Mitigations

Phase: Architecture and Design

Description:

Avoid making decisions based on names of resources (e.g. files) if those resources can have alternate names.

Phase: Implementation

Description:

Phase: Implementation

Description:

Inputs should be decoded and canonicalized to the application’s current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174). Such errors could be used to bypass allowlist validation schemes by introducing dangerous inputs after they have been checked.

Phase:

Description:

Canonicalize the name to match that of the file system’s representation of the name. This can sometimes be achieved with an available API (e.g. in Win32 the GetFullPathName function).

CVE References

CVE-2004-0815
- “/.////” in pathname collapses to absolute path.

CVE-2005-3123
- “/.//..//////././” is collapsed into “/.././” after “..” and “//” sequences are removed.

CVE-2002-0325
- “…/…//” collapsed to “…” due to removal of “./” in web server.

CVE-2002-0784
- chain: HTTP server protects against “..” but allows “.” variants such as “////./../…/”. If the server removes “/..” sequences, the result would collapse into an unsafe value “////../” (CWE-182).

CVE-2005-2169
- MFV. Regular expression intended to protect against directory traversal reduces “…/…//” to “../”.

CVE-2001-1157
- XSS protection mechanism strips a

Read Time:45 Second

Description

The software validates data before it has been filtered, which prevents the software from detecting data that becomes invalid after the filtering step.

This can be used by an attacker to bypass the validation and launch attacks that expose weaknesses that would otherwise be prevented, such as injection.

Modes of Introduction:

– Implementation

Related Weaknesses

CWE-179

Consequences

Access Control: Bypass Protection Mechanism

Potential Mitigations

Phase: Implementation, Architecture and Design

Description:

Inputs should be decoded and canonicalized to the application’s current internal representation before being filtered.

CVE References

CVE-2002-0934
- Directory traversal vulnerability allows remote attackers to read or modify arbitrary files via invalid characters between two . (dot) characters, which are filtered and result in a “..” sequence.

CVE-2003-0282
- Directory traversal vulnerability allows attackers to overwrite arbitrary files via invalid characters between two . (dot) characters, which are filtered and result in a “..” sequence.

CWE

CWE-180 – Incorrect Behavior Order: Validate Before Canonicalize

May 26, 2022 rocco

Read Time:1 Minute, 8 Second

Description

The software validates input before it is canonicalized, which prevents the software from detecting data that becomes invalid after the canonicalization step.

This can be used by an attacker to bypass the validation and launch attacks that expose weaknesses that would otherwise be prevented, such as injection.

Modes of Introduction:

– Implementation

Related Weaknesses

CWE-179

Consequences

Access Control: Bypass Protection Mechanism

Potential Mitigations

Phase: Implementation

Description:

CVE References

CVE-2002-0433
- Product allows remote attackers to view restricted files via an HTTP request containing a “*” (wildcard or asterisk) character.

CVE-2003-0332
- Product modifies the first two letters of a filename extension after performing a security check, which allows remote attackers to bypass authentication via a filename with a .ats extension instead of a .hts extension.

CVE-2002-0802
- Database consumes an extra character when processing a character that cannot be converted, which could remove an escape character from the query and make the application subject to SQL injection attacks.

CVE-2000-0191
- Overlaps “fakechild/../realchild”

CVE-2004-2363
- Product checks URI for “

CWE

CWE-179 – Incorrect Behavior Order: Early Validation

May 26, 2022 rocco

Read Time:1 Minute, 25 Second

Description

The software validates input before applying protection mechanisms that modify the input, which could allow an attacker to bypass the validation via dangerous inputs that only arise after the modification.

Software needs to validate data at the proper time, after data has been canonicalized and cleansed. Early validation is susceptible to various manipulations that result in dangerous inputs that are produced by canonicalization and cleansing.

Modes of Introduction:

– Implementation

Related Weaknesses

CWE-20
CWE-696

Consequences

Access Control, Integrity: Bypass Protection Mechanism, Execute Unauthorized Code or Commands

An attacker could include dangerous input that bypasses validation protection mechanisms which can be used to launch various attacks including injection attacks, execute arbitrary code or cause other unintended behavior.

Potential Mitigations

Phase: Implementation

Description:

CVE References

CVE-2002-0433
- Product allows remote attackers to view restricted files via an HTTP request containing a “*” (wildcard or asterisk) character.

CVE-2003-0332
- Product modifies the first two letters of a filename extension after performing a security check, which allows remote attackers to bypass authentication via a filename with a .ats extension instead of a .hts extension.

CVE-2002-0802
- Database consumes an extra character when processing a character that cannot be converted, which could remove an escape character from the query and make the application subject to SQL injection attacks.

CVE-2000-0191
- Overlaps “fakechild/../realchild”

CVE-2004-2363
- Product checks URI for “

CVE-2002-0934
- Directory traversal vulnerability allows remote attackers to read or modify arbitrary files via invalid characters between two . (dot) characters, which are filtered and result in a “..” sequence.

CVE-2003-0282
- Directory traversal vulnerability allows attackers to overwrite arbitrary files via invalid characters between two . (dot) characters, which are filtered and result in a “..” sequence.

CWE

CWE-178 – Improper Handling of Case Sensitivity

May 26, 2022 rocco

Read Time:2 Minute, 48 Second

Description

The software does not properly account for differences in case sensitivity when accessing or determining the properties of a resource, leading to inconsistent results.

Modes of Introduction:

– Implementation

Related Weaknesses

CWE-706
CWE-706
CWE-433
CWE-289

Consequences

Access Control: Bypass Protection Mechanism

Potential Mitigations

Phase: Architecture and Design

Description:

Avoid making decisions based on names of resources (e.g. files) if those resources can have alternate names.

Phase: Implementation

Description:

Phase: Implementation

Description:

CVE References

CVE-2000-0499
- Application server allows attackers to bypass execution of a jsp page and read the source code using an upper case JSP extension in the request.

CVE-2000-0497
- The server is case sensitive, so filetype handlers treat .jsp and .JSP as different extensions. JSP source code may be read because .JSP defaults to the filetype “text”.

CVE-2000-0498
- The server is case sensitive, so filetype handlers treat .jsp and .JSP as different extensions. JSP source code may be read because .JSP defaults to the filetype “text”.

CVE-2001-0766
- A URL that contains some characters whose case is not matched by the server’s filters may bypass access restrictions because the case-insensitive file system will then handle the request after it bypasses the case sensitive filter.

CVE-2001-0795
- Server allows remote attackers to obtain source code of CGI scripts via URLs that contain MS-DOS conventions such as (1) upper case letters or (2) 8.3 file names.

CVE-2001-1238
- Task Manager does not allow local users to end processes with uppercase letters named (1) winlogon.exe, (2) csrss.exe, (3) smss.exe and (4) services.exe via the Process tab which could allow local users to install Trojan horses that cannot be stopped.

CVE-2003-0411
- chain: Code was ported from a case-sensitive Unix platform to a case-insensitive Windows platform where filetype handlers treat .jsp and .JSP as different extensions. JSP source code may be read because .JSP defaults to the filetype “text”.

CVE-2002-0485
- Leads to interpretation error

CVE-1999-0239
- Directories may be listed because lower case web requests are not properly handled by the server.

CVE-2005-0269
- File extension check in forum software only verifies extensions that contain all lowercase letters, which allows remote attackers to upload arbitrary files via file extensions that include uppercase letters.

CVE-2004-1083
- Web server restricts access to files in a case sensitive manner, but the filesystem accesses files in a case insensitive manner, which allows remote attackers to read privileged files using alternate capitalization.

CVE-2002-2119
- Case insensitive passwords lead to search space reduction.

CVE-2004-2214
- HTTP server allows bypass of access restrictions using URIs with mixed case.

CVE-2004-2154
- Mixed upper/lowercase allows bypass of ACLs.

CVE-2005-4509
- Bypass malicious script detection by using tokens that aren’t case sensitive.

CVE-2002-1820
- Mixed case problem allows “admin” to have “Admin” rights (alternate name property).

CVE-2007-3365
- Chain: uppercase file extensions causes web server to return script source code instead of executing the script.

CWE

CWE-177 – Improper Handling of URL Encoding (Hex Encoding)

May 26, 2022 rocco

Read Time:1 Minute, 21 Second

Description

The software does not properly handle when all or part of an input has been URL encoded.

Modes of Introduction:

– Implementation

Related Weaknesses

CWE-172

Consequences

Integrity: Unexpected State

Potential Mitigations

Phase: Architecture and Design

Description:

Avoid making decisions based on names of resources (e.g. files) if those resources can have alternate names.

Phase: Implementation

Description:

Phase: Implementation

Description:

CVE References

CVE-2000-0900
- Hex-encoded path traversal variants – “%2e%2e”, “%2e%2e%2f”, “%5c%2e%2e”

CVE-2005-2256
- Hex-encoded path traversal variants – “%2e%2e”, “%2e%2e%2f”, “%5c%2e%2e”

CVE-2004-2121
- Hex-encoded path traversal variants – “%2e%2e”, “%2e%2e%2f”, “%5c%2e%2e”

CVE-2004-0280
- “%20” (encoded space)

CVE-2003-0424
- “%20” (encoded space)

CVE-2001-0693
- “%20” (encoded space)

CVE-2001-0778
- “%20” (encoded space)

CVE-2002-1831
- Crash via hex-encoded space “%20”.

CVE-2000-0671
- “%00” (encoded null)

CVE-2004-0189
- “%00” (encoded null)

CVE-2002-1291
- “%00” (encoded null)

CVE-2002-1031
- “%00” (encoded null)

CVE-2001-1140
- “%00” (encoded null)

CVE-2004-0760
- “%00” (encoded null)

CVE-2002-1025
- “%00” (encoded null)

CVE-2002-1213
- “%2f” (encoded slash)

CVE-2004-0072
- “%5c” (encoded backslash) and “%2e” (encoded dot) sequences

CVE-2004-0847
- “%5c” (encoded backslash)

CVE-2002-1575
- “%0a” (overlaps CRLF)

Description

Related Weaknesses

Consequences

Potential Mitigations

CVE References

Description

Related Weaknesses

Consequences

Potential Mitigations

CVE References

Description

Related Weaknesses

Consequences

Potential Mitigations

CVE References

Description

Related Weaknesses

Consequences

Potential Mitigations

CVE References

Description

Related Weaknesses

Consequences

Potential Mitigations

CVE References

Description

Related Weaknesses

Consequences

Potential Mitigations

CVE References

Description

Related Weaknesses

Consequences

Potential Mitigations

CVE References

Description

Related Weaknesses

Consequences

Potential Mitigations

CVE References

Description

Related Weaknesses

Consequences

Potential Mitigations

CVE References

Description

Related Weaknesses

Consequences

Potential Mitigations

CVE References

News, Advisories and much more