CVE-2025-62727VulnerabilityPublished 28 Oct 2025Updated 4 Nov 2025

CVE-2025-62727: Kludex starlette · Inefficient Algorithmic Complexity

Affects Kludex starletteSource CVE Database V5

Not known to be exploited · CVSS 7.5 High : upgrade to 0.49.1 soon.

Data as of 25 Oct 2026, 19:02 UTC

CVSS 3.1 base score

7.5High

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

EPSS: 0.8% chance of exploitation in 30 days – higher than 56% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 0.49.1

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

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

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: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 28 Oct 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 2026-10-25.

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 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 Kludex starlette to 0.49.1.

Affected software

Product	Affected	Fixed in
PyPIstarlette`pkg:pypi/starlette`Other threats	Affected >=0.39.0 <0.49.1	Fixed in 0.49.1

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

AI-suggested

1. Upgrade all Starlette deployments to version 0.49.1 or later immediately to apply the fix that optimizes Range header processing and eliminates the quadratic-time complexity. 2. Implement strict rate limiting on HTTP requests targeting file-serving endpoints to reduce the risk of CPU exhaustion from malicious Range headers. 3. Monitor web server and application logs for abnormal or excessive Range header usage patterns indicative of exploitation attempts. 4. Use Web Application Firewalls (WAFs) or reverse proxies capable of detecting and blocking suspicious Range headers or malformed requests. 5. Conduct regular security audits and penetration testing focused on file-serving endpoints to identify potential exploitation vectors. 6. Consider disabling support for HTTP Range headers on endpoints where partial content delivery is not required. 7. Educate development and operations teams about this vulnerability and ensure patch management processes prioritize such high-severity issues. 8. In environments where immediate upgrade is not feasible, deploy mitigations such as CPU usage limits per request or container resource constraints to limit impact.

Description

Starlette is a lightweight ASGI framework/toolkit. Starting in version 0.39.0 and prior to version 0.49.1 , an unauthenticated attacker can send a crafted HTTP Range header that triggers quadratic-time processing in Starlette's FileResponse Range parsing/merging logic. This enables CPU exhaustion per request, causing denial‑of‑service for endpoints serving files (e.g., StaticFiles or any use of FileResponse). This vulnerability is fixed in 0.49.1.

Impact

For European organizations, this vulnerability poses a significant risk to the availability of web applications that use Starlette versions between 0.39.0 and 0.49.1 to serve static files or file responses. Public-facing services that rely on these endpoints can be targeted by attackers to cause denial-of-service, resulting in downtime, degraded user experience, and potential loss of business or reputation. Critical infrastructure or services that depend on Starlette for file delivery could face operational disruptions. Since the vulnerability does not require authentication or user interaction, it can be exploited by any remote attacker, increasing the attack surface. The CPU exhaustion caused by the quadratic-time processing can also lead to increased operational costs due to resource overuse and may trigger cascading failures in dependent systems. European organizations in sectors such as finance, government, healthcare, and e-commerce that rely on Python-based web frameworks are particularly vulnerable. Additionally, regulatory requirements around service availability and incident response in Europe heighten the importance of timely mitigation.

CWE-407Inefficient Algorithmic Complexity (opens in a new tab)
Class weaknessLikelihood of exploit: Low
An algorithm in a product has an inefficient worst-case computational complexity that may be detrimental to system performance and can be triggered by an attacker, typically using crafted manipulations that ensure that the worst case is being reached.
OWASP Cheat Sheets
File Upload (opens in a new tab)
OWASP ASVS 4.0.3
V12.1.1 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

Community reviews

Loading reviews…

Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 5 Nov 2025, 00:56 UTC

WeaknessesCWE-407

Technical details

References

Community reviews

Related threats