Starlette vulnerable to O(n^2) DoS via Range header merging in starlette.responses.FileResponse
Kludex · starlette
Official source article: GitHub GHSA-7F5H-V6XP-FCQ8 ↗. Check the applicable product and release in the original source.
7.5HighCVSS 3.1
Recommended action
Within 7 days
High technical severity with public exploit material referenced by a structured source; prioritise exposed affected systems while verifying vendor guidance.
Published severityHigh→Operational priority:Critical, raised one band.upgradedsince 4 Nov 2025
Evidence used
No CISA KEV confirmation is currently recorded.
A structured source references public exploit or proof-of-concept material.
The selected CVSS metric records a network-reachable, unauthenticated path with no user interaction.
EPSS is 0.68% for the current model date.
Compensating controls
Validate the affected product branch and deploy the verified fixed release.
Restrict the affected network interface to trusted sources where business-safe.
Increase monitoring for the attack path and post-exploitation behaviour described in the report.
Verification
Confirm that the asset runs Kludex starlette and falls inside the recorded affected range.
Verify the installed build against the product-specific fixed version after deployment.
Validate exposure, authentication requirements and compensating controls in the actual environment.
Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
Distribution package intelligence
Release-specific package status
Debian, ubuntu findings are scoped to the named distribution, release and source package. An absent finding does not mean a package is unaffected.
5 package states
Repository candidate not checked
A published vendor fix does not prove that a matching update is enabled and installable on a particular asset. Confirm the local package candidate before scheduling remediation.
Distribution release
Source package
Vendor state
Fixed version
Evidence
Debian trixietrixie · source
starlette
Vendor fix publishedDebian records a fixed source-package version for this release.
These OSV and GitHub advisory ranges apply only to the named package and ecosystem. A listed fixed version is not a universal product patch or proof that an update is installed.
Structured product status and remediation from the issuing vendor. Product-state explanations are always visible; large lists can be searched or downloaded.
1 current
CVE-2025-62727 · CSAF 2.0 · revision 3 · finalRed Hat Product Securitystarlette: Starlette DoS via Range header merging
17 known affected
The vendor explicitly identifies these products as affected by this CVE.
openshift-lightspeed/lightspeed-ocp-rag-rhel9 as a component of OpenShift Lightspeed
openshift-lightspeed/lightspeed-service-api-rhel9 as a component of OpenShift Lightspeed
rhaiis/vllm-spyre-rhel9 as a component of Red Hat AI Inference Server
rhaiis/vllm-tpu-rhel9 as a component of Red Hat AI Inference Server
rhelai1/bootc-amd-rhel9 as a component of Red Hat Enterprise Linux AI (RHEL AI)
rhelai1/bootc-aws-nvidia-rhel9 as a component of Red Hat Enterprise Linux AI (RHEL AI)
rhelai1/bootc-azure-amd-rhel9 as a component of Red Hat Enterprise Linux AI (RHEL AI)
rhelai1/bootc-azure-nvidia-rhel9 as a component of Red Hat Enterprise Linux AI (RHEL AI)
rhelai1/bootc-gcp-nvidia-rhel9 as a component of Red Hat Enterprise Linux AI (RHEL AI)
rhelai1/bootc-intel-rhel9 as a component of Red Hat Enterprise Linux AI (RHEL AI)
rhelai1/bootc-nvidia-rhel9 as a component of Red Hat Enterprise Linux AI (RHEL AI)
rhelai1/instructlab-amd-rhel9 as a component of Red Hat Enterprise Linux AI (RHEL AI)
Summary
A denial of service vulnerability has been discovered in the python Starlette framework. an unauthenticated attacker can send a crafted HTTP Range header that triggers quadratic-time processing in Starlette's FileResponse Range parsing/merging logic. This induces CPU exhaustion per request, causing a denial‑of‑service for endpoints serving files.
Remediation
For more information visit https://access.redhat.com/errata/RHSA-2025:23080
Optional official sources
National CERT insights ?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.
Choose official national sources for this report. Each advisory shows its original language. Your selection is remembered on this device and included in shared links.
Official European source
ENISA European Vulnerability Database
Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.
1 current
ENISA EUVD identifier
EUVD-2025-36555
No EUVD known-exploited evidence
ENISA has published the identifier mapping but no EUVD description has been stored yet.
EUVD state
Present in the current official mapping
Known exploitation
Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score
Not supplied in the stored EUVD record
Advisory evidence
No linked advisory details stored yet
Recommended actionWithin 7 days
High technical severity with public exploit material referenced by a structured source; prioritise exposed affected systems while verifying vendor guidance.
Patch available
01
What, why and how
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.
What
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.
Why
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.
How
An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.
What
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.
Why
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.
How
An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.
02
Exploit reality and attack path
CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.
Observed exploitation ?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.No confirmed evidence
No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.
Public PoC / exploit material ?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.Reference recorded
CISA Vulnrichment records proof-of-concept exploitation in its SSVC data. BlackTree has not independently executed or validated exploit material.
Likely attack path
a network path → Inefficient Algorithmic Complexity → cause the confidentiality, integrity or availability impact described by the vendor
Attack surface
Network
Privileges required
None: unauthenticated exploitation is possible
User interaction
None
Attack complexity
Low: no specialised conditions are recorded
Security boundary
Unchanged: impact remains within the vulnerable component's security authority
Weakness ?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-407: Inefficient Algorithmic Complexity. 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.
CVSS vector ?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Common Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.
AVNetworkAttack vector: The vulnerable component can be reached over a network.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.PRNonePrivileges required: The attacker does not need an account or existing privileges.UINoneUser interaction: No action by another user is required.SUnchangedScope: The security impact remains within the vulnerable component's authority.CNoneConfidentiality impact: No direct loss is represented by this metric.INoneIntegrity impact: No direct loss is represented by this metric.AHighAvailability impact: A successful attack can cause a major loss.
Post-exploitation / living off the land
No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.
Only matched European and national findings are included. Language selectors and unavailable sources are omitted.
ENISA EUVD · EUVD-2025-36555Official EUVD mapping
0 linked advisory records.
Official EUVD record ↗Cyber Security Agency of Singapore · English · CSA-SB-20251029Security Bulletin 29 Oct 2025
The Cyber Security Agency of Singapore included this CVE in its official Security Bulletin 29 Oct 2025, published on 29 October 2025. Open the linked bulletin for the product, severity and reference information published in that issue.
Official advisory ↗CERT-FR · French · CERTFR-2026-AVI-0327Multiples vulnérabilités dans les produits IBM
Official advisory ↗CERT-FR · French · CERTFR-2025-AVI-1138Multiples vulnérabilités dans VMware Tanzu Platform
d?id=CVE-2025-61723
Référence CVE CVE-2025-61724
https://www.cve.org/CVERecord?id=CVE-2025-61724
Référence CVE CVE-2025-61725
https://www.cve.org/CVERecord?id=CVE-2025-61725
Référence CVE CVE-2025-61727
https://www.cve.org/CVERecord?id=CVE-2025-61727
Référence CVE CVE-2025-61729
https://www.cve.org/CVERecord?id=CVE-2025-61729
Référence CVE CVE-2025-62164
https://www.cve.org/CVERecord?id=CVE-2025-62164
Référence CVE CVE-2025-62372
https://www.cve.org/CVERecord?id=CVE-2025-62372
Référence CVE CVE-2025-62426
https://www.cve.org/CVERecord?id=CVE-2025-62426
Référence CVE CVE-2025-62593
https://www.cve.org/CVERecord?id=CVE-2025-62593
Référence CVE CVE-2025-62727
https://www.cve.org/CVERecord?id=CVE-2025-62727
Référence CVE CVE-2025-66448
https://www.cve.org/CVERecord?id=CVE-2025-66448
Gestion détaillée du document
le 26 décembre 2025
Version initiale
Alertes
Avis
Bulletins d’actualités
Mentions légales
Conditions générales
À propos
Contact
cyber.gouv.fr
service-public.fr
legifrance.gouv.fr
info.gouv.fr
france.fr
info.gouv.fr/risques
Premier Ministre / Secrétariat Général de la Défense et de la Sécurité Nationale / Agence nationale de la
sécurité des systèmes d'information
Operational remediation based on structured source evidence.
Status ?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
For more information visit https://access.redhat.com/errata/RHSA-2025:23080
Workaround
No verified workaround is recorded. If business-safe, reduce exposure to the affected interface and allow only trusted sources until authoritative guidance is available.
04
Evidence and provenance
Published 28 Oct 2025 · Last source change 4 Nov 2025, 17:41 UTC · CWE-407 · Inefficient Algorithmic Complexity
CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source ?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.FIRST · tracked since 2026-08-14
European sourceENISA EUVD · EUVD-2025-36555
Product sourceVendor CSAF · Red Hat Product Security
Remediation sourceVendor CSAF · Red Hat Product Security
CWE sourceCNA
NVD statusNVD not scheduled
Core structured fields are present and their contributing authorities are shown above.
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.