VulnerabilityPublished 8 Dec 2025

CVE-2025-66202: withastro astro · Use of Non-Canonical URL Paths for Authorization Decisions

Affects withastro astroSource CVE Database V5

Mentioned vulnerabilities

CVE-2025-64765

Not known to be exploited · CVSS 6.5 Medium : upgrade to 5.15.8 when convenient.

Data as of 26 Oct 2026, 14:05 UTC

CVSS 3.1 base score

6.5Medium

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

EPSS: 0.3% chance of exploitation in 30 days – higher than 24% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 5.15.8

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
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: None: The vulnerable system can be exploited without any interaction from any user.
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 8 Dec 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: 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 26 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.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, 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 withastro astro to 5.15.8.

Affected software

Product	Affected	Fixed in
npmastro`pkg:npm/astro`Other threats	Affected <5.15.8	Fixed in 5.15.8

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

AI-suggested

European organizations should immediately upgrade all Astro framework instances to version 5.15.8 or later, where the double URL encoding bypass is fully fixed. In addition to patching, developers should audit middleware and authorization logic to ensure that URL paths are fully normalized and canonicalized before any security decisions are made. Implement strict input validation and decoding routines that handle multiple layers of encoding. Employ web application firewalls (WAFs) with rules to detect and block suspicious double-encoded URL patterns. Conduct thorough security testing, including fuzzing and penetration testing focused on URL encoding edge cases. Monitor web server logs for unusual URL encoding patterns that could indicate exploitation attempts. Finally, maintain an inventory of applications using Astro to prioritize patching and risk assessment efforts.

Description

Astro is a web framework. Versions 5.15.7 and below have a double URL encoding bypass which allows any unauthenticated attacker to bypass path-based authentication checks in Astro middleware, granting unauthorized access to protected routes. While the original CVE-2025-64765 was fixed in v5.15.8, the fix is insufficient as it only decodes once. By using double-encoded URLs, attackers can still bypass authentication and access any route protected by middleware pathname checks. This issue is fixed in version 5.15.8.

Impact

For European organizations, this vulnerability can lead to unauthorized access to protected web application routes, potentially exposing sensitive data or allowing unauthorized actions within applications built on vulnerable Astro versions. The impact primarily affects confidentiality and integrity, as attackers can bypass authentication controls without credentials or user interaction. This can result in data leakage, unauthorized data modification, or access to administrative functions. Since Astro is a modern web framework used in building performant websites and applications, organizations in sectors such as finance, e-commerce, government, and technology that rely on Astro middleware for access control are at risk. The vulnerability does not directly impact availability but could facilitate further attacks that degrade service or compromise systems. The lack of known exploits currently provides a window for proactive mitigation, but the ease of exploitation and remote nature of the vulnerability mean that attackers could develop exploits rapidly once the vulnerability becomes widely known.

CWE-647Use of Non-Canonical URL Paths for Authorization Decisions (opens in a new tab)
Variant weaknessLikelihood of exploit: High
The product defines policy namespaces and makes authorization decisions based on the assumption that a URL is canonical. This can allow a non-canonical URL to bypass the authorization.
Architecture and Design
Make access control policy based on path information in canonical form. Use very restrictive regular expressions to validate that the path is in the expected form.
Architecture and Design
Reject all alternate path encodings that are not in the expected canonical form.
OWASP ASVS 4.0.3
V8.3.8 (opens in a new tab)
V13.4.2 (opens in a new tab)
V7.2.2 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 16 Dec 2025, 06:02 UTC

WeaknessesCWE-647

Technical details

References

Community reviews

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