CVE-2026-34231

A Cross-site Scripting (XSS) vulnerability exists in the {% attrs %} template tag of the slippers Django package. When a context variable containing untrusted data is passed to {% attrs %}, the value is interpolated into an HTML attribute string without escaping, allowing an attacker to break out of the attribute context and inject arbitrary HTML or JavaScript into the rendered page.

Vulnerability details

Root cause

AttrsNode is a custom Node subclass registered via register.tag(). Unlike register.simple_tag(), which automatically applies conditional_escape() when autoescape is on, custom Node.render() methods receive no automatic escaping and are fully responsible for sanitising their output. attr_string() fails to do this:

def attr_string(key: str, value: Any):
    if isinstance(value, bool):
        return key if value else ""
    key = key.replace("_", "-")
    return f'{key}="{value}"'   # value is not escaped

Attack scenario

Given a template that uses {% attrs %} with a user-supplied value:

{% load slippers %}
<input {% attrs type placeholder %}>

render(request, "search.html", {"placeholder": request.GET.get("q", "")})

An attacker crafting a request with q=" onmouseover="alert(document.cookie)" x=" produces:

<input type="text" placeholder="" onmouseover="alert(document.cookie)" x="">

Any template that passes values derived from user input, database content, or other untrusted sources to {% attrs %} is vulnerable. Successful exploitation can lead to session hijacking, credential theft, arbitrary actions on behalf of the victim, and page defacement.

Untrusted input is rendered as active markup in a victim's browser, which can run script in their session. Typical impact: session or credential theft, and actions taken as the user.

CVE-2026-34231 has a CVSS score of 6.1 (Medium). The vector is network-reachable, no privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.6.3); upgrading removes the vulnerable code path.

Kodem intelligence

Replace the f-string in attr_string() with format_html(), which escapes both key and value:

from django.utils.html import format_html

def attr_string(key: str, value: Any):
    if isinstance(value, bool):
        return key if value else ""
    key = key.replace("_", "-")
    return format_html('{}="{}"', key, value)

Until a patch is available, sanitise untrusted values before passing them to {% attrs %}, for example with django.utils.html.escape() in the view layer.

1. What is CVE-2026-34231? CVE-2026-34231 is a medium-severity cross-site scripting (XSS) vulnerability in slippers (pip), affecting versions <= 0.6.2. It is fixed in 0.6.3. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
2. How severe is CVE-2026-34231? CVE-2026-34231 has a CVSS score of 6.1 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of slippers are affected by CVE-2026-34231? slippers (pip) versions <= 0.6.2 is affected.
4. Is there a fix for CVE-2026-34231? Yes. CVE-2026-34231 is fixed in 0.6.3. Upgrade to this version or later.
5. Is CVE-2026-34231 exploitable, and should I be worried? Whether CVE-2026-34231 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-34231 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-34231? Upgrade slippers to 0.6.3 or later.