# [HIGH] CVE-2025-29927 Authorization Bypass in Next.js Middleware

**Source:** Snyk
**Published:** 2025-03-23
**Article:** https://snyk.io/blog/cve-2025-29927-authorization-bypass-in-next-js-middleware/

## Threat Profile

Snyk Blog In this article
Written by Liran Tal 
March 23, 2025
0 mins read 
CVE-2025-29927 Authorization Bypass in Next.js Middleware On Friday morning, March 21, 2025, at 9:00 a.m. UTC, a security advisory identified as CVE-2025-29927 was published. It cited a critical 9.1 severity vulnerability for mainstream Next.js applications.
Next.js versions considered vulnerable:
Next.js 15.x versions before15.2.3
Next.js 14.x versions before 14.2.25
Next.js 13.x versions before 13.5.9
All Next.js versi…

## Indicators of Compromise (high-fidelity only)

- **CVE:** `CVE-2025-29927`

## MITRE ATT&CK Techniques

- **T1190** — Exploit Public-Facing Application
- **T1195.002** — Compromise Software Supply Chain
- **T1204.002** — User Execution: Malicious File
- **T1078** — Valid Accounts
- **T1556** — Modify Authentication Process

## Kill chain phases observed

_(none detected from narrative keywords)_

## Recommended hunts

### Next.js CVE-2025-29927 middleware bypass via x-middleware-subrequest header

`UC_948_3` · phase: **exploit** · confidence: **High** · AI-generated for this article

**Splunk SPL (CIM):**
```spl
| tstats `summariesonly` count min(_time) as firstTime max(_time) as lastTime values(Web.url) as urls values(Web.http_method) as methods values(Web.status) as statuses dc(Web.url) as url_count from datamodel=Web where Web.http_user_agent=* (Web.http_request_headers="*x-middleware-subrequest*" OR Web.http_request_headers="*middleware:middleware:middleware:middleware:middleware*" OR Web.http_request_headers="*x-middleware-subrequest: middleware*") by Web.src Web.dest Web.http_user_agent Web.url_domain | `drop_dm_object_name(Web)` | where url_count >= 1
```

**Defender KQL:**
```kql
// Defender Advanced Hunting does not natively capture inbound HTTP request headers for self-hosted web servers.
// This detection is implemented on Sentinel/SIEM web-tier telemetry instead — see sentinel_kql.
// For Defender, the closest pivot is host-side: a Next.js node process receiving traffic that is followed by
// post-auth-only commands (DB dumps, secret reads) from an unauthenticated session — too noisy to express here.
```

### Trusted vendor binary / installer launching unusual children

`UC_SUPPLY_CHAIN` · phase: **exploit** · confidence: **Medium**

**Splunk SPL (CIM):**
```spl
| tstats `summariesonly` count min(_time) as firstTime max(_time) as lastTime
    from datamodel=Endpoint.Processes
    where Processes.parent_process_name IN ("setup.exe","installer.exe","update.exe")
      AND Processes.process_name IN ("powershell.exe","cmd.exe","rundll32.exe","regsvr32.exe","mshta.exe","wscript.exe","cscript.exe","wmic.exe","bitsadmin.exe")
    by Processes.dest, Processes.user, Processes.parent_process_name, Processes.process_name, Processes.process
| `drop_dm_object_name(Processes)`
```

**Defender KQL:**
```kql
DeviceProcessEvents
| where Timestamp > ago(7d)
| where AccountName !endswith "$"
| where InitiatingProcessFileName in~ ("setup.exe","installer.exe","update.exe")
| where FileName in~ ("powershell.exe","cmd.exe","rundll32.exe","regsvr32.exe","mshta.exe","wscript.exe","cscript.exe","wmic.exe","bitsadmin.exe")
| project Timestamp, DeviceName, AccountName, InitiatingProcessFileName, FileName, ProcessCommandLine
```

### Article-specific behavioural hunt — CVE-2025-29927 Authorization Bypass in Next.js Middleware

`UC_948_2` · phase: **exploit** · confidence: **High**

**Splunk SPL (CIM):**
```spl
``` Article-specific bespoke detection — CVE-2025-29927 Authorization Bypass in Next.js Middleware ```
| tstats `summariesonly` count earliest(_time) AS firstTime latest(_time) AS lastTime
    from datamodel=Endpoint.Processes
    where (Processes.process_name IN ("next.js","node.js"))
    by Processes.dest, Processes.user, Processes.process_name,
       Processes.process, Processes.parent_process_name, Processes.process_path
| `drop_dm_object_name(Processes)`
| `security_content_ctime(firstTime)`
| append [
| tstats `summariesonly` count
    from datamodel=Endpoint.Filesystem
    where Filesystem.action IN ("created","modified")
      AND (Filesystem.file_name IN ("next.js","node.js"))
    by Filesystem.dest, Filesystem.user, Filesystem.process_name,
       Filesystem.file_path, Filesystem.file_name
| `drop_dm_object_name(Filesystem)`
]
```

**Defender KQL:**
```kql
// Article-specific bespoke detection — CVE-2025-29927 Authorization Bypass in Next.js Middleware
// Hunts the actual binaries / paths / commandline fragments named
// in the article instead of a generic technique-class template.
DeviceProcessEvents
| where Timestamp > ago(30d)
| where (FileName in~ ("next.js", "node.js"))
| project Timestamp, DeviceName, AccountName, FileName,
          FolderPath, ProcessCommandLine,
          InitiatingProcessFileName, InitiatingProcessCommandLine
| order by Timestamp desc

// File-creation events for the named binaries / paths
DeviceFileEvents
| where Timestamp > ago(30d)
| where ActionType in ("FileCreated","FileModified")
| where (FileName in~ ("next.js", "node.js"))
| project Timestamp, DeviceName, AccountName, FolderPath,
          FileName, ActionType, InitiatingProcessFileName,
          InitiatingProcessCommandLine
| order by Timestamp desc
```

### IOC-driven hunts (use shared templates)

These are standard IOC-substitution hunts — the canonical SPL and KQL live once in [`_TEMPLATES.md`](../_TEMPLATES.md), so we don't repeat the same boilerplate on every CVE / hash / network-IOC briefing.

- **Asset exposure — vulnerability matches article CVE(s)** ([template](../_TEMPLATES.md#asset-exposure)) — phase: **recon**, confidence: **High**
  - CVE(s): `CVE-2025-29927`


## Why this matters

Severity classified as **HIGH** based on: CVE present, 4 use case(s) fired, 5 technique(s) inferred. Read the full article for actor attribution, tooling details, and any defanged IOCs in the body that aren't visible in the RSS summary.