CVE-2023-23934 | Wrkzeug's incorrect parsing of nameless cookies leads to __Host- cookies bypass

Werkzeug is a comprehensive WSGI web application library. Browsers may allow "nameless" cookies that look like `=value` instead of `key=value`. A vulnerable browser may allow a compromised application on an adjacent subdomain to exploit this to set a cookie like `=__Host-test=bad` for another subdomain. Werkzeug prior to 2.2.3 will parse the cookie `=__Host-test=bad` as __Host-test=bad`. If a Werkzeug application is running next to a vulnerable or malicious subdomain which sets such a cookie using a vulnerable browser, the Werkzeug application will see the bad cookie value but the valid cookie key. The issue is fixed in Werkzeug 2.2.3.

Published: 2023-02-14 Last update: 2024-11-21 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2023-23934 is rated Low Risk (26/100): CVSS Low severity, with low exploitation likelihood (EPSS 0.60%). Monitor for updates and reassess as exploit intelligence or EPSS changes.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2023-23934

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.27% 0.60% +0.33%
2 2026-03-04 0.24% 0.27% +0.03%
3 2026-02-07 — 0.24% —

Full EPSS history (16 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2023-23934

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
2.6 3.1 LOW
CVSS:3.1/AV:A/AC:H/PR:N/UI:R/S:U/C:N/I:L/A:N Click to expand
Attack vector (AV:A)
Attacker has to be nearby on the network—same office, same link, that vibe—not the whole wide internet.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:R)
A real person has to do something—click, install, enable—otherwise it doesn’t land.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:L)
Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N)
Service keeps running; no real outage angle.
 1.2 1.4 [email protected]
3.5 3.1 LOW
CVSS:3.1/AV:A/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N Click to expand
Attack vector (AV:A)
Attacker has to be nearby on the network—same office, same link, that vibe—not the whole wide internet.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:R)
A real person has to do something—click, install, enable—otherwise it doesn’t land.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:L)
Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N)
Service keeps running; no real outage angle.
 2.1 1.4 [email protected]

Weakness enumeration for CVE-2023-23934

GitHub Security Advisory for CVE-2023-23934

GHSA-px8h-6qxv-m22q · Severity: low · Ecosystem: pip — Incorrect parsing of nameless cookies leads to __Host- cookies bypass

OS Trackers for CVE-2023-23934

vendor priority summary link
debian not yet assigned CVE-2023-23934 not yet assigned priority: Debian including 1 source packages (python-werkzeug), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2023-23934
redhat low — https://access.redhat.com/security/cve/CVE-2023-23934
suse low CVE-2023-23934 severity low: SUSE including 3 source package names (python-Werkzeug, python2-Werkzeug, python3-Werkzeug), 44 product×package rows across 25 product lines (HPE Helion OpenStack 8, SUSE CaaS Platform 4.0, … (25 product lines)): Will Not Fix 44. https://www.suse.com/security/cve/CVE-2023-23934/
ubuntu medium CVE-2023-23934 medium priority: Ubuntu including 1 source packages (python-werkzeug), 8 status rows across 8 suites (bionic, focal, jammy, kinetic, lunar, trusty, upstream, xenial): released 7, ignored 1. https://ubuntu.com/security/CVE-2023-23934

Affected software / configurations for CVE-2023-23934

Vendor Product Version Raw CPE
palletsprojects werkzeug < 2.2.3 cpe:2.3:a:palletsprojects:werkzeug:*:*:*:*:*:*:*:*

References for CVE-2023-23934

cvelogic Threat Intelligence