CVE-2023-4639 is a high-severity (CVSS 7.4) CWE-444 vulnerability in undertow. A fix is available for undertow — see the affected versions and patch details below.
Undertow incorrectly parses cookies
Exploitation Status
No confirmed exploitation observed yet
- A successful exploit gives an attacker total control of the affected component, not partial access.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2023-4639.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2023-4639 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 378,156 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
undertowReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Debian:13 packages — download data is not available via public APIs for these ecosystems.
Description
A flaw was found in Undertow, which incorrectly parses cookies with certain value-delimiting characters in incoming requests. This issue could allow an attacker to construct a cookie value to exfiltrate HttpOnly cookie values or spoof arbitrary additional cookie values, leading to unauthorized data access or modification. The main threat from this flaw impacts data confidentiality and integrity.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦Debian:13 | undertow | all versions | 2.3.18-1 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for undertow, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update undertow to 2.3.18-1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2023-4639 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2023-4639 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2023-4639. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
| Product | Fixed in | Advisory |
|---|---|---|
| Migration Toolkit for Runtimes 1 on RHEL 8 | mtr/mtr-operator-bundle:1.2-23 | RHSA-2024:3919 |
| Red Hat JBoss Enterprise Application Platform | io.undertow/undertow-core:2.2.30.SP1-redhat-00001 | RHSA-2024:1677 |
| Red Hat JBoss Enterprise Application Platform 7.4 for RHEL 8 | eap7-undertow-0:2.2.30-1.SP1_redhat_00001.1.el8eap | RHSA-2024:1675 |
| Red Hat JBoss Enterprise Application Platform 7.4 for RHEL 9 | eap7-undertow-0:2.2.30-1.SP1_redhat_00001.1.el9eap | RHSA-2024:1676 |
| Red Hat JBoss Enterprise Application Platform 7.4 on RHEL 7 | eap7-undertow-0:2.2.30-1.SP1_redhat_00001.1.el7eap | RHSA-2024:1674 |
| Red Hat JBoss Enterprise Application Platform 8 | undertow | RHSA-2024:2763 |
| Red Hat JBoss Enterprise Application Platform 8.0 for RHEL 8 | eap8-undertow-0:2.3.11-1.SP1_redhat_00001.1.el8eap | RHSA-2024:2764 |
Frequently Asked Questions
Is CVE-2023-4639 in your dependencies?
O3 Security finds CVE-2023-4639 across Debian:13 dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.