CVE-2023-4639 – This vulnerability in Undertow allows attackers... (How to Fix)

Q: What is the severity of CVE-2023-4639?

CVE-2023-4639 has a CVSS score of 7.4 (HIGH). This vulnerability in Undertow allows attackers to manipulate cookie parsing to exfiltrate HttpOnly cookie values or inject arbitrary cookies. This can lead to unauthorized data access or modification, affecting data confidentiality and integrity. Systems using vulnerable versions of Undertow are affected.

📋 TL;DR

This vulnerability in Undertow allows attackers to manipulate cookie parsing to exfiltrate HttpOnly cookie values or inject arbitrary cookies. This can lead to unauthorized data access or modification, affecting data confidentiality and integrity. Systems using vulnerable versions of Undertow are affected.

💻 Affected Systems

Products:

Undertow

Versions: Versions before the patched releases referenced in Red Hat advisories

Operating Systems: Linux (primarily Red Hat Enterprise Linux variants)

Default Config Vulnerable: ⚠️ Yes

Notes: Affects Undertow as used in Red Hat products like JBoss EAP, WildFly, and related middleware. Default configurations are vulnerable.

⚠️ Manual Verification Required

This CVE does not have specific version information in our database, so automatic vulnerability detection cannot determine if your system is affected.

Why? The CVE database entry doesn't specify which versions are vulnerable (no version ranges provided by the vendor/NVD).

🔒 Custom verification scripts are available for registered users. Sign up free to download automated test scripts.

Recommended Actions:

Review the CVE details at NVD
Check vendor security advisories for your specific version
Test if the vulnerability is exploitable in your environment
Consider updating to the latest version as a precaution

⚠️ Risk & Real-World Impact

🔴

Worst Case

Attackers could steal session tokens or authentication cookies, leading to full account compromise and unauthorized data access/modification across affected applications.

🟠

Likely Case

Session hijacking or privilege escalation through cookie manipulation, potentially allowing unauthorized actions within web applications.

🟢

If Mitigated

Limited impact with proper network segmentation and monitoring, though cookie-based attacks could still occur within the application layer.

🌐 Internet-Facing: HIGH

🏢 Internal Only: MEDIUM

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

Exploitation requires sending specially crafted HTTP requests with malicious cookie values. No authentication needed if the application is accessible.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Refer to Red Hat advisories RHSA-2024:1674 through RHSA-2024:1677 and RHSA-2024:2763 for specific patched versions

Vendor Advisory: https://access.redhat.com/errata/RHSA-2024:1674

Restart Required: Yes

Instructions:

1. Identify affected Undertow installations. 2. Apply relevant Red Hat security updates via yum update or similar. 3. Restart affected services/containers. 4. Verify the patch is applied.

🔧 Temporary Workarounds

Input Validation Filter

all

Implement custom filters to sanitize cookie values before processing by Undertow

Implement Java servlet filter or Undertow handler to reject cookies with suspicious delimiter characters

🧯 If You Can't Patch

Implement WAF rules to block requests with malformed cookie headers containing delimiter characters
Restrict network access to affected applications using firewalls or network segmentation

🔍 How to Verify

Check if Vulnerable:

Check Undertow version against patched versions in Red Hat advisories. For RHEL: rpm -qa | grep undertow

Check Version:

rpm -q undertow (on RHEL systems) or check application server version details

Verify Fix Applied:

Confirm updated package version matches patched versions in advisories and test with crafted cookie requests

📡 Detection & Monitoring

Log Indicators:

HTTP requests with unusual cookie values containing delimiter characters like semicolons, commas, or quotes
Unexpected cookie parsing errors in application logs

Network Indicators:

HTTP traffic with malformed Cookie headers containing multiple delimiter sequences

SIEM Query:

source="web_logs" AND (Cookie:*;*;* OR Cookie:*,*,* OR Cookie:*"*")

📊 Metadata

CVE ID: CVE-2023-4639

CVSS v3 Score: 7.4 (HIGH)

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

CWE: CWE-444

Published: November 17, 2024

Last Updated: February 7, 2025

🔗 References

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