Description
Templates do not properly consider backticks (`) as Javascript string delimiters, and do not escape them as expected. Backticks are used, since ES6, for JS template literals. If a template contains a Go template action within a Javascript template literal, the contents of the action can be used to terminate the literal, injecting arbitrary Javascript code into the Go template. As ES6 template literals are rather complex, and themselves can do string interpolation, the decision was made to simply disallow Go template actions from being used inside of them (e.g. "var a = {{.}}"), since there is no obviously safe way to allow this behavior. This takes the same approach as github.com/google/safehtml. With fix, Template.Parse returns an Error when it encounters templates like this, with an ErrorCode of value 12. This ErrorCode is currently unexported, but will be exported in the release of Go 1.21. Users who rely on the previous behavior can re-enable it using the GODEBUG flag jstmpllitinterp=1, with the caveat that backticks will now be escaped. This should be used with caution.
EPSS Score:
6%
Comprehensive Technical Analysis of EUVD-2023-28554
1. Vulnerability Assessment and Severity Evaluation
Vulnerability Description: The vulnerability pertains to the improper handling of backticks (`) as JavaScript string delimiters in Go templates. Specifically, Go template actions within JavaScript template literals can be exploited to inject arbitrary JavaScript code. This issue arises because ES6 template literals are complex and can perform string interpolation, making it difficult to safely allow Go template actions within them.
Severity Evaluation:
The vulnerability has a CVSS Base Score of 9.8, which is considered critical. The CVSS vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H indicates:
- Attack Vector (AV): Network (N)
- Attack Complexity (AC): Low (L)
- Privileges Required (PR): None (N)
- User Interaction (UI): None (N)
- Scope (S): Unchanged (U)
- Confidentiality (C): High (H)
- Integrity (I): High (H)
- Availability (A): High (H)
This high severity score underscores the potential for significant impact on confidentiality, integrity, and availability.
2. Potential Attack Vectors and Exploitation Methods
Attack Vectors:
- Code Injection: An attacker could inject malicious JavaScript code by exploiting the improper handling of backticks in Go templates. This could lead to Cross-Site Scripting (XSS) attacks.
- Template Manipulation: By manipulating the template literals, an attacker could execute arbitrary code, potentially leading to data exfiltration, unauthorized access, or denial of service.
Exploitation Methods:
- Crafted Input: An attacker could craft input that includes backticks and Go template actions to terminate the literal and inject malicious code.
- Web Application Exploits: In web applications using Go templates, an attacker could exploit this vulnerability to inject scripts that steal user data, manipulate the DOM, or perform other malicious actions.
3. Affected Systems and Software Versions
Affected Software:
- Go standard library:
html/template- Versions:
0 < 1.19.8 - Versions:
1.20.0-0 < 1.20.3
- Versions:
Affected Systems:
- Any system or application that uses the affected versions of the Go standard library for template rendering, particularly those that handle user input in templates.
4. Recommended Mitigation Strategies
Immediate Mitigation:
- Upgrade: Upgrade to a patched version of the Go standard library (
html/templateversion1.19.8or1.20.3and above). - Disable Feature: Use the
GODEBUGflagjstmpllitinterp=1with caution to re-enable the previous behavior, ensuring backticks are escaped.
Long-Term Mitigation:
- Code Review: Conduct thorough code reviews to ensure that templates do not contain Go template actions within JavaScript template literals.
- Input Validation: Implement robust input validation and sanitization to prevent injection attacks.
- Security Training: Educate developers on secure coding practices, particularly around template handling and JavaScript injection risks.
5. Impact on European Cybersecurity Landscape
Regulatory Compliance:
- Organizations must ensure compliance with regulations such as GDPR, which mandates the protection of personal data. This vulnerability could lead to data breaches, resulting in regulatory penalties.
Critical Infrastructure:
- Critical infrastructure sectors using Go for web applications must prioritize patching to prevent potential disruptions or data breaches.
Public Trust:
- Public trust in digital services could be eroded if this vulnerability is exploited, leading to financial and reputational damage for affected organizations.
6. Technical Details for Security Professionals
Technical Overview:
- Template Literals: ES6 template literals use backticks (
) and allow for string interpolation using${expression}`. - Go Template Actions: Go template actions (e.g.,
{{.}}) can be used to inject dynamic content into templates.
Detection and Monitoring:
- Logging: Implement comprehensive logging to detect and monitor any unusual template rendering activities.
- Intrusion Detection Systems (IDS): Use IDS to detect and alert on potential injection attempts.
Patch Details:
- Error Handling: The fix ensures that
Template.Parsereturns an error with anErrorCodeof value 12 when it encounters templates with Go template actions within JavaScript template literals. - Error Code Export: The
ErrorCodewill be exported in the release of Go 1.21, allowing for better error handling and debugging.
References:
- Go Issue Tracker
- Go Change Log
- Golang Announce Group
- Go Vulnerability Database
- Gentoo Security Advisory
- NVD CVE Entry
- NetApp Security Advisory
By addressing this vulnerability promptly and comprehensively, organizations can mitigate the risk of exploitation and ensure the security and integrity of their systems.