VulnerabilityPublished 13 Aug 2026Updated 29 Oct 2026

CVE-2025-67724: Jupyterlab · Tornado vulnerable to Header Injection and XSS via reason argument

Affects jupyterlabSource GCVE Database

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Authoritative record:CVE-2025-67724· Medium 5.4

Not known to be exploited · CVSS 5.4 Medium : upgrade to 4.5.1 when convenient.

Data as of 30 Oct 2026, 09:00 UTC

CVSS 3.1 base score

5.4Medium

How severe the flaw is on the 0–10 CVSS scale.

Patch: Available – fixed in 4.5.1

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: Required
Scope: Unchanged
Confidentiality: Low
Integrity: Low
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: Required: Successful exploitation of this vulnerability requires a user to take some action before the vulnerability can be exploited.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to the impacted component.
Integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 12 Dec 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 29 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade jupyterlab to 4.5.1.

Affected software

Product	Affected	Fixed in
Homebrewjupyterlab`pkg:brew/jupyterlab`Other threats	Affected >=1.2.0 <4.5.1	Fixed in 4.5.1

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Upgrade JupyterLab to version 4.5.1 or later, which includes Tornado 6.5.3 or newer where the vulnerability is fixed. Alternatively, avoid passing untrusted input to the 'reason' argument in HTTPError or set_status calls. Since the 'reason' argument is rarely required and not used in HTTP/2, it can generally be omitted. For general-purpose error messages, use the 'log_message' argument instead of 'reason'.

Description

JupyterLab versions from 1.2.0 up to but not including 4.5.1 are affected by a vulnerability in the Tornado web framework (CVE-2025-67724) where the 'reason' argument used in HTTP status responses can lead to header injection or reflected cross-site scripting (XSS). This occurs if untrusted input is passed to the 'reason' argument, which is then included unescaped in HTTP headers or the default error page HTML. The vulnerability allows remote attackers to execute arbitrary JavaScript in users' browsers when they view the error page. The issue is fixed in Tornado 6.5.3 and JupyterLab 4.5.1. Mitigation includes upgrading to fixed versions or avoiding use of untrusted data in the 'reason' argument.

Impact

Remote attackers can exploit this vulnerability to execute arbitrary JavaScript in the browsers of users who view the affected application's error page, potentially leading to session token theft, cross-site request forgery (CSRF) escalation, UI spoofing, or other client-side attacks. The impact is limited to applications that explicitly reflect untrusted input into the 'reason' argument. There is no indication of known exploitation in the wild.

Summary

The vulnerability in Tornado versions prior to 6.5.3, affecting JupyterLab versions >=1.2.0 <4.5.1, arises from improper handling of the 'reason' argument used in RequestHandler.set_status and tornado.web.HTTPError. If untrusted data is passed as the 'reason' phrase, it is inserted unescaped into HTTP headers and the default error page HTML, enabling header injection (CWE-644) and reflected XSS (CWE-79). Exploitation requires that an attacker can cause the application to raise HTTPError or set_status with attacker-controlled 'reason' data, such as via a query parameter. The vulnerability is mitigated by upgrading to Tornado 6.5.3 or newer (JupyterLab 4.5.1 or later) or by ensuring untrusted input is not used in the 'reason' argument. The 'reason' argument is rarely necessary and can be omitted or replaced with 'log_message' for error logging.

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Affected software

Description

AI analysisMachine-generated, updated 30 Oct 2026, 09:00 UTC

Technical details

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