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CVE Record

CVE-2026-9520: blitz-js blitz Sign-in LoginForm.tsx cross site scripting

A weakness has been identified in blitz-js blitz up to 3.0.2 on GitHub. This impacts an unknown function of the file packages/generator/templates/app/src/app/auth/components/LoginForm.tsx of the component Sign-in. This manipulation of the argument Next causes cross site scripting. It is possible to initiate the attack remotely. The exploit has been made available to the public and could be used for attacks. The vendor was contacted early about this disclosure but did not respond in any way.

MediumCVSS 5.3Not KEV-listed Updated
Discuss exposure Back to CVEs
Glexia's Take moderate

Analyst readout for executives and security teams

Plain-English summary

CVE-2026-9520 is a medium-severity issue in blitz-js Blitz sign-in code. A manipulated Next argument in LoginForm.tsx can lead to cross-site scripting. The business risk is session abuse or misleading sign-in flows if affected generated code is present. Public exploit material exists, but the provided sources do not show active exploitation.

Executive priority

Treat as a targeted web-app hygiene issue, not a crisis. Prioritize applications using Blitz authentication templates, especially internet-facing sign-in pages. Public exploit availability raises urgency, but medium severity, user interaction, and lack of KEV evidence keep this below emergency response level.

Technical view

Sources describe XSS in packages/generator/templates/app/src/app/auth/components/LoginForm.tsx for Blitz 3.0.0 through 3.0.2. The issue involves handling of the Next argument in the Sign-in component. CVSS v4.0 is 5.3 with network attack vector, low complexity, no privileges, and user interaction required. CWE-79 and CWE-94 are listed.

Likely exposure

Exposure appears limited to Blitz 3.0.0, 3.0.1, and 3.0.2 users, especially applications using the generated sign-in LoginForm.tsx template. Because generated files may be copied into applications, dependency version alone may not fully prove or disprove exposure.

Exploitation context

The source bundle says exploit material is public and remote attack initiation is possible. CVSS requires user interaction, and KEV is false. No cited source in the bundle confirms active exploitation in the wild.

Researcher notes

The public record is incomplete: the vulnerable function is unnamed, no vendor response is reported, and no patch is identified in the provided sources. Validate exposure in generated application code, not only package metadata. Avoid assuming active attacks without additional evidence.

Mitigation direction

  • Inventory Blitz versions and generated auth components across applications.
  • Check vendor guidance and upgrade when an official fixed release is available.
  • Audit LoginForm.tsx handling of Next or redirect parameters.
  • Restrict redirect targets to trusted internal paths only.
  • Ensure reflected values are encoded or not rendered into executable contexts.

Validation and detection

  • Review lockfiles for Blitz 3.0.0, 3.0.1, or 3.0.2.
  • Search generated application code for LoginForm.tsx sign-in components.
  • Confirm Next parameter handling cannot inject script-capable content.
  • Verify sign-in redirects reject external or malformed destinations.
  • Check security monitoring for suspicious sign-in redirect or XSS reports.
Prepared
Confidence
medium
Sources
6

Public sources used

Based on public source material and reviewed before publication.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cwe · medium confidence lookup

CWE-79: User-session and phishing behavior lookup

Client-side and session-facing weaknesses should be reviewed alongside initial-access and user-execution behaviors. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

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cwe · medium confidence lookup

CWE-94: Code execution behavior lookup

Code execution and unsafe deserialization weaknesses often justify reviewing execution behavior and process telemetry. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

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cve · low confidence lookup

CVE-2026-9520 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

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Vulnerability profile CVE Program record
Severity
Medium
CVSS
5.3 (4.0)
Known Exploited
No
Published

Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:P

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

4 CVSS vectors
6 Timeline events
1 ADP providers
5 Source links

SSVC decision data

CISA-ADP CISA Coordinator
Timestamp
Version
2.0.3
Exploitation: pocAutomatable: noTechnical Impact: partial

CVSS vector scores

4 official scores

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

Score Version Severity Vector Exploit Impact Source
5.3 CVSS 4.0 Medium CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:P — — VulDB
5 CVSS 2.0 Medium AV:N/AC:L/Au:N/C:N/I:P/A:N/E:POC/RL:ND/RC:UR 10 2.9 VulDB
4.3 CVSS 3.1 Medium CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N/E:P/RL:X/RC:R 2.8 1.4 VulDB
4.3 CVSS 3.0 Medium CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N/E:P/RL:X/RC:R 2.8 1.4 VulDB

Vulnerability scoring details

Base CVSS 4.0 score

5.3 Medium
CVSS 4.0 vector shape for CVE-2026-9520 Attack VectorAttack ComplexityAttack RequirementsPrivileges RequiredUser InteractionVS ConfidentialityVS IntegrityVS AvailabilitySS ConfidentialitySS IntegritySS Availability

Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:P

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Attack Requirements
NonePresent
Privileges Required
NoneLowHigh
User Interaction
NonePassiveActive
VS Confidentiality
HighLowNone
VS Integrity
HighLowNone
VS Availability
HighLowNone
SS Confidentiality
HighLowNone
SS Integrity
HighLowNone
SS Availability
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. Source timeline VulDB

    Advisory disclosed

  2. Source timeline VulDB

    VulDB entry created

  3. CVE reserved CVE Program

    The CVE ID was reserved by the assigning CNA.

  4. Source timeline VulDB

    VulDB entry last update

  5. CVE published CVE Program

    The CVE record was published.

  6. CVE updated CVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADP CISA ADP Vulnrichment
other:ssvc

Source materials

Affected products

Products and packages named in the record

Vendor Product Version / package Status
blitz-js blitz 3.0.0, 3.0.1, 3.0.2 Listed
Weakness

CWE details

CWE-79CWE-94

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.

CWE-79 · source CWE mapping

Improper Neutralization of Input During Web Page Generation

Improper Neutralization of Input During Web Page Generation represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

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CWE-94 · source CWE mapping

CWE mapping pending import

This CVE carries a CWE mapping that will resolve to a full Glexia CWE intelligence page after the official CWE import is complete.

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