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CWE-838

Inappropriate Encoding for Output Context

BaseIncompleteSimple18 CVEs
The product uses or specifies an encoding when generating output to a downstream component, but the specified encoding is not the same as the encoding that is expected by the downstream component.

Extended description

This weakness can cause the downstream component to use a decoding method that produces different data than what the product intended to send. When the wrong encoding is used - even if closely related - the downstream component could decode the data incorrectly. This can have security consequences when the provided boundaries between control and data are inadvertently broken, because the resulting data could introduce control characters or special elements that were not sent by the product. The resulting data could then be used to bypass protection mechanisms such as input validation, and enable injection attacks. While using output encoding is essential for ensuring that communications between components are accurate, the use of the wrong encoding - even if closely related - could cause the downstream component to misinterpret the output. For example, HTML entity encoding is used for elements in the HTML body of a web page. However, a programmer might use entity encoding when generating output for that is used within an attribute of an HTML tag, which could contain functional Javascript that is not affected by the HTML encoding. While web applications have received the most attention for this problem, this weakness could potentially apply to any type of product that uses a communications stream that could support multiple encodings.

Common consequences1

  • IntegrityConfidentialityAvailabilityModify Application DataExecute Unauthorized Code or Commands

    An attacker could modify the structure of the message or data being sent to the downstream component, possibly injecting commands.

Potential mitigations3

  1. Implementation

    Use context-aware encoding. That is, understand which encoding is being used by the downstream component, and ensure that this encoding is used. If an encoding can be specified, do so, instead of assuming that the default encoding is the same as the default being assumed by the downstream component.

  2. Architecture and Design

    Where possible, use communications protocols or data formats that provide strict boundaries between control and data. If this is not feasible, ensure that the protocols or formats allow the communicating components to explicitly state which encoding/decoding method is being used. Some template frameworks provide built-in support.

  3. Architecture and Design

    Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. For example, consider using the ESAPI Encoding control [REF-45] or a similar tool, library, or framework. These will help the programmer encode outputs in a manner less prone to error. Note that some template mechanisms provide built-in support for the appropriate encoding.

Relationships2

CVEs referencing this CWE18

CVEDescriptionSeverityEPSSFlagsModified
CVE-2019-6110

In OpenSSH 7.9, due to accepting and displaying arbitrary stderr output from the server, a malicious server (or Man-in-The-Middle attacker) can manipulate the client output, for example to use ANSI control codes to hide additional files being transferred.

MEDIUM6.8
21%p97
PoC
2026-06-17
CVE-2020-10996

An issue was discovered in Percona XtraDB Cluster before 5.7.28-31.41.2. A bundled script inadvertently sets a static transition_key for SST processes in place of the random key expected.

HIGH8.1
1.50%p72
2026-06-17
CVE-2019-18981

Pimcore before 6.2.2 lacks an Access Denied outcome for a certain scenario of an incorrect recipient ID of a notification.

CRITICAL9.8
1.39%p70
2026-06-17
CVE-2023-6512

Inappropriate implementation in Web Browser UI in Google Chrome prior to 120.0.6099.62 allowed a remote attacker to potentially spoof the contents of an iframe dialog context menu via a crafted HTML page. (Chromium security severity: Low)

MEDIUM6.5
1.28%p67
2026-06-17
CVE-2020-7292

Inappropriate Encoding for output context vulnerability in McAfee Web Gateway (MWG) prior to 9.2.1 allows a remote attacker to cause MWG to return an ambiguous redirect response via getting a user to click on a malicious URL.

MEDIUM4.3
0.86%p55
2026-06-17
CVE-2025-4052

Inappropriate implementation in DevTools in Google Chrome prior to 136.0.7103.59 allowed a remote attacker who convinced a user to engage in specific UI gestures to bypass discretionary access control via a crafted HTML page. (Chromium security severity: Low)

CRITICAL9.8
0.58%p45
2026-06-17
CVE-2023-3735

Inappropriate implementation in Web API Permission Prompts in Google Chrome prior to 115.0.5790.98 allowed a remote attacker to obfuscate security UI via a crafted HTML page. (Chromium security severity: Medium)

MEDIUM4.3
0.58%p45
2026-06-17
CVE-2020-29135

cPanel before 90.0.17 has multiple instances of URL parameter injection (SEC-567).

MEDIUM4.1
0.58%p45
2026-06-17
CVE-2024-11702

Copying sensitive information from Private Browsing tabs on Android, such as passwords, may have inadvertently stored data in the cloud-based clipboard history if enabled. This vulnerability affects Firefox < 133 and Thunderbird < 133.

HIGH7.5
0.54%p43
2026-06-17
CVE-2022-43407

Jenkins Pipeline: Input Step Plugin 451.vf1a_a_4f405289 and earlier does not restrict or sanitize the optionally specified ID of the 'input' step, which is used for the URLs that process user interactions for the given 'input' step (proceed or abort) and is not correctly encoded, allowing attackers able to configure Pipelines to have Jenkins build URLs from 'input' step IDs that would bypass the CSRF protection of any target URL in Jenkins when the 'input' step is interacted with.

HIGH8.8
0.53%p42
2026-06-17
CVE-2022-43408

Jenkins Pipeline: Stage View Plugin 2.26 and earlier does not correctly encode the ID of 'input' steps when using it to generate URLs to proceed or abort Pipeline builds, allowing attackers able to configure Pipelines to specify 'input' step IDs resulting in URLs that would bypass the CSRF protection of any target URL in Jenkins.

MEDIUM6.5
0.47%p39
2026-06-17
CVE-2026-53641

FOSSBilling is a free, open-source billing and client management system. Versions 0.6.0 through 0.7.2 have a stored cross-site scripting (XSS) vulnerability in the client-facing email history views of FOSSBilling. Email HTML content (`content_html`) is rendered into a JavaScript template literal using the `|raw` filter, bypassing all output escaping. An attacker with admin access can inject malicious JavaScript payloads into email content that execute in the browser of any client who views their email history. Version 0.8.0 contains a fix. Some workarounds are available. Restrict admin account access, audit email content in the database for suspicious payloads, and/or monitor client accounts for unusual activity.

NONE
0.44%p37
2026-07-08
CVE-2018-9862

util.c in runV 1.0.0 for Docker mishandles a numeric username, which allows attackers to obtain root access by leveraging the presence of an initial numeric value on an /etc/passwd line, and then issuing a "docker exec" command with that value in the -u argument, a similar issue to CVE-2016-3697.

NONE
0.42%p35
2026-06-17
CVE-2024-34006

The site log report required additional encoding of event descriptions to ensure any HTML in the content is displayed in plaintext instead of being rendered.

MEDIUM4.3
0.35%p28
2026-06-17
CVE-2023-5770

Proofpoint Enterprise Protection contains a vulnerability in the email delivery agent that allows an unauthenticated attacker to inject improperly encoded HTML into the email body of a message through the email subject. The vulnerability is caused by inappropriate encoding when rewriting the email before delivery.This issue affects Proofpoint Enterprise Protection: from 8.20.2 before patch 4809, from 8.20.0 before patch 4805, from 8.18.6 before patch 4804 and all other prior versions.

MEDIUM5.4
0.34%p27
2026-06-17
CVE-2026-47079

Inappropriate Encoding for Output Context vulnerability in joshnuss xml_builder (XmlBuilder module) allows Content Spoofing, Cross-site Scripting. This vulnerability is associated with program files lib/xml_builder.ex and program routines XmlBuilder.generate/1, XmlBuilder.generate/2, XmlBuilder.escape_string/1, XmlBuilder.escape_entity/1. XmlBuilder.generate/1 does not escape literal & characters in text or attribute values when they are followed by an entity-like token (lt;, gt;, amp;, quot;, apos;). As a result, attacker-supplied input such as &lt;script&gt; is emitted verbatim into the serialized XML rather than being escaped to &amp;lt;script&amp;gt;. When a downstream XML parser later reads the document, it decodes the entity sequences into the literal characters <script>, promoting inert-looking text into real markup. This allows an attacker to bypass upstream filters that block raw < and > characters, injecting markup into any downstream consumer that parses the produced XML and renders the text content in a markup-sensitive context (HTML, SVG, RSS/Atom feeds). Both element text and attribute values are affected. This issue affects xml_builder: from 0.0.6 before 2.4.1.

NONE
0.14%p4
2026-08-24
CVE-2026-55859

MariaDB Connector/R2DBC is a non-blocking MariaDB and MySQL client implemented in Java. Prior to 1.4.1, org.mariadb:r2dbc-mariadb encodes and decodes all character data under the assumption that the connection character set is UTF-8. A server can announce a mid-session change to character_set_client through the OK-packet session-state-tracking mechanism, including through SET NAMES executed by a stored routine or trigger, server configuration, or a hostile or man-in-the-middle server. If the new character set is not UTF-8, the driver continues to exchange UTF-8 while the server interprets the same bytes under a different encoding, causing silent data corruption and a client/server charset-confusion mismatch that can defeat byte-wise quoting or escaping. The fix accepts only utf8, utf8mb3, or utf8mb4 after initialization; any other value raises R2dbcNonTransientResourceException with SQLState 08000 and closes the connection. This issue is fixed in version 1.4.1.

MEDIUM5.9no EPSS
2026-08-28
CVE-2026-55858

MariaDB Connector/J is used to connect applications developed in Java to MariaDB and MySQL databases. Prior to 2.7.14, 3.3.5, 3.4.3, and 3.5.9, the connector encodes and decodes protocol text and performs client-side escaping under the assumption that the connection character set is UTF-8. The server can report a mid-session change to character_set_client through OK-packet session-state tracking, including a change caused by SET NAMES, a stored routine or trigger, server configuration, or a hostile server. If character_set_client changes to a non-UTF-8 value, the driver continues to read and write UTF-8 while the server interprets the same bytes under another encoding, causing silent data corruption and a client/server charset-confusion mismatch that can defeat byte-wise quoting or escaping. The fix accepts only utf8, utf8mb3, or utf8mb4 after initialization; any other value causes SQLException with SQLState 08000 and closes the connection. This issue is fixed in versions 2.7.14, 3.3.5, 3.4.3, and 3.5.9.

MEDIUM5.9no EPSS
2026-08-28