While adding general comments is very useful, some programmers tend to leave important data, such as: filenames related to the web application, old links or links which were not meant to be browsed by users, old code fragments, etc.
An attacker who finds these comments can map the application's structure and files, expose hidden parts of the site, and study the fragments of code to reverse engineer the application, which may help develop further attacks against the site.

Primary

Implementation

Confidentiality
Read Application Data

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.)
High

Distribution
Remove comments which have sensitive information about the design/implementation of the application. Some of the comments may be exposed to the user and affect the security posture of the application.

The following comment, embedded in a JSP, will be displayed in the resulting HTML output.

<!-- FIXME: calling this with more than 30 args kills the JDBC server -->

CVE-2007-6197
Version numbers and internal hostnames leaked in HTML comments.
https://www.cve.org/CVERecord?id=CVE-2007-6197

CVE-2007-4072
CMS places full pathname of server in HTML comment.
https://www.cve.org/CVERecord?id=CVE-2007-4072

CVE-2009-2431
blog software leaks real username in HTML comment.
https://www.cve.org/CVERecord?id=CVE-2009-2431

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

Anonymous Tool Vendor (under NDA)
2007-05-07
Draft 6
2007-05-07

Sean Eidemiller
Cigital
2008-07-01
added/updated demonstrative examples

Eric Dalci
Cigital
2008-07-01
updated Potential_Mitigations, Time_of_Introduction

CWE Content Team
MITRE
2008-09-08
updated Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2008-10-14
updated Description

CWE Content Team
MITRE
2009-03-10
updated Demonstrative_Examples

CWE Content Team
MITRE
2009-07-27
updated Observed_Examples, Taxonomy_Mappings

CWE Content Team
MITRE
2011-03-29
updated Name

CWE Content Team
MITRE
2011-06-01
updated Common_Consequences

CWE Content Team
MITRE
2012-05-11
updated Relationships

CWE Content Team
MITRE
2012-10-30
updated Potential_Mitigations

CWE Content Team
MITRE
2014-07-30
updated Relationships

CWE Content Team
MITRE
2017-11-08
updated Demonstrative_Examples

CWE Content Team
MITRE
2020-02-24
updated Name, Relationships

CWE Content Team
MITRE
2023-04-27
updated Detection_Factors, Relationships

CWE Content Team
MITRE
2023-06-29
updated Mapping_Notes

CWE Content Team
MITRE
2025-12-11
4.19
2025-12-11
updated Applicable_Platforms, Relationships, Weakness_Ordinalities

Information Leak Through Comments
Information Exposure Through Comments