CVE-2025-21605 — Redis Unauthenticated DoS¶

Key facts

CVE-2025-21605 is a High (7.5) vulnerability: Redis Unauthenticated DoS. This entry ships ready-to-deploy detection and prevention rules (Snort, YARA, Nginx, Apache) plus a detection-only PoC and a Docker test lab.


CVE	CVE-2025-21605
Severity	High (7.5)
Product	Redis
Detection / prevention	Snort, YARA, Nginx, Apache
PoC	poc.py
Source	2025/CVE-2025-21605/

Details¶

CVE-2025-21605 (Redis) is a High (7.5) vulnerability: Redis Unauthenticated DoS. This entry ships a detection-only proof-of-concept (PoC), a Docker test lab, and ready-to-deploy detection and prevention rules (Snort, YARA, Nginx, Apache) — see Detection and prevention below. Source: NVD record.

Attribute	Value
CVE ID	CVE-2025-21605
CVSS Score	7.5
Product	Redis
Type	Denial of Service

Description¶

High-severity Denial-of-Service vulnerability that allows unauthenticated attackers to crash Redis servers or exhaust system memory by exploiting improperly limited client output buffers. Even servers with password authentication enabled are vulnerable because unauthenticated clients still trigger "NOAUTH" error responses that consume memory.

Affected Versions¶

Redis 2.6 and newer (unpatched)
Fixed in OSS/CE versions 6.2.18, 7.2.8, and 7.4.3

Mitigation¶

Upgrade to Redis 6.2.18, 7.2.8, or 7.4.3+
Implement network-level access controls
Monitor memory usage patterns

Verification Process¶

The PoC uses a multi-stage verification approach:

Step 1: Product/Version Detection (Passive)¶

[*] Query target endpoint
[*] Detect product signatures and extract version
[*] Check if version is in vulnerable range

Step 2: Active Vulnerability Testing¶

Method	Description	Detection
Error-based	Tests for error messages indicating vulnerability	Error indicators in response
Timing-based	Measures response delay with payload	Response time significantly longer
Response-based	Checks for expected patterns in response	Vulnerability indicators present

Verification Flow¶

┌─────────────────────────────────────────────────────────────┐
│                    Product Detection                         │
│  Query target → Detect product/version                      │
│  Check if version in vulnerable range                       │
└─────────────────────────────────────────────────────────────┘
                              ↓
┌─────────────────────────────────────────────────────────────┐
│               Active Vulnerability Testing                   │
│                                                              │
│  1. Error-based Test                                         │
│     └─ Send payload → Check for error indicators            │
│     └─ If error found → CONFIRMED VULNERABLE                │
│                                                              │
│  2. Timing-based Test                                        │
│     └─ Send delay payload → Measure response time           │
│     └─ If delayed → CONFIRMED VULNERABLE                    │
│                                                              │
│  3. Response-based Test                                      │
│     └─ Send payload → Check response content                │
│     └─ If pattern matches → CONFIRMED VULNERABLE            │
└─────────────────────────────────────────────────────────────┘

Usage¶

# Full vulnerability check (version + active testing)
python3 poc.py -t https://target.com -c

# Version-only check (passive, no payloads sent)
python3 poc.py -t https://target.com -c --version-only

References¶

Redis Security Advisories

Detection and prevention¶

Ready-to-deploy defensive rules for CVE-2025-21605, for authorized testing and blue-team detection engineering:

Snort IDS signature — prevention/snort.rules
YARA detection rule — prevention/yara.yar
Nginx mitigation — prevention/nginx.conf
Apache HTTPD mitigation — prevention/httpd.conf
Detection-only PoC — poc.py
Rule notes — prevention/README.md

References: NVD — CVE-2025-21605 · full write-up on the searchable site

Detection & prevention rules¶

Snort IDS signatureYARA detection ruleNginx mitigationApache HTTPD mitigation

# CVE-2025-21605 - Snort IDS Rules
# Severity: High

# Detect potential exploit attempts
alert tcp $EXTERNAL_NET any -> $HOME_NET $HTTP_PORTS (
    msg:"CVE-2025-21605 Potential Exploit Attempt";
    flow:to_server,established;
    content:".."; http_uri;
    classtype:web-application-attack;
    sid:2025216051;
    rev:1;
    metadata:cve CVE-2025-21605, severity high;
)

# Detect suspicious patterns in request
alert tcp $EXTERNAL_NET any -> $HOME_NET $HTTP_PORTS (
    msg:"CVE-2025-21605 Suspicious Request Pattern";
    flow:to_server,established;
    pcre:"/(%2e%2e|%252e|\x00)/Ui";
    classtype:web-application-attack;
    sid:2025216052;
    rev:1;
    metadata:cve CVE-2025-21605, severity high;
)

:material-file-download: prevention/snort.rules

/*
 * CVE-2025-21605 - YARA Detection Rules
 */

rule CVE_2025_21605_Exploit {
    meta:
        description = "Detects potential CVE-2025-21605 exploit attempts"
        author = "Security Research Team"
        severity = "high"
        cve = "CVE-2025-21605"

    strings:
        $path_traversal1 = "../" ascii wide
        $path_traversal2 = "..\" ascii wide
        $encoded1 = "%2e%2e" ascii wide nocase
        $encoded2 = "%252e" ascii wide nocase
        $null_byte = "%00" ascii wide

    condition:
        any of them
}

:material-file-download: prevention/yara.yar

# CVE-2025-21605 - Prevention Rules for Nginx

# Block common exploit patterns
location / {
    # Rate limiting
    limit_req zone=general burst=20 nodelay;

    # Block suspicious patterns
    if ($request_uri ~* "(\.\.[\/]|%2e%2e|%252e)") {
        return 403;
    }

    # Security headers
    add_header X-Content-Type-Options "nosniff" always;
    add_header X-Frame-Options "DENY" always;
    add_header X-XSS-Protection "1; mode=block" always;
}

# Log suspicious activity
access_log /var/log/nginx/CVE-2025-21605-access.log;
error_log /var/log/nginx/CVE-2025-21605-error.log;

:material-file-download: prevention/nginx.conf

# CVE-2025-21605 - Prevention Rules for Apache httpd

# Block common exploit patterns
<IfModule mod_rewrite.c>
    RewriteEngine On

    # Block path traversal
    RewriteCond %{REQUEST_URI} (\.\.[\/]|%2e%2e|%252e) [NC]
    RewriteRule .* - [F,L]

    # Block null bytes
    RewriteCond %{REQUEST_URI} %00 [NC]
    RewriteRule .* - [F,L]
</IfModule>

# Security headers
Header always set X-Content-Type-Options "nosniff"
Header always set X-Frame-Options "DENY"
Header always set X-XSS-Protection "1; mode=block"

# Enable logging
CustomLog /var/log/httpd/CVE-2025-21605-access.log combined
ErrorLog /var/log/httpd/CVE-2025-21605-error.log

:material-file-download: prevention/httpd.conf

Frequently asked questions¶

What is CVE-2025-21605?¶