CVE-2026-3644 | Incomplete control character validation in http.cookies

The fix for CVE-2026-0672, which rejected control characters in http.cookies.Morsel, was incomplete. The Morsel.update(), |= operator, and unpickling paths were not patched, allowing control characters to bypass input validation. Additionally, BaseCookie.js_output() lacked the output validation applied to BaseCookie.output().

Published: 2026-03-16 Last update: 2026-06-04 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-3644 is rated Low Risk (27/100): CVSS Medium severity, with low exploitation likelihood (EPSS 0.03%). 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-2026-3644

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 2026-06-05 0.05% 0.03% -0.02%
2 2026-05-22 0.04% 0.05% +0.01%
3 2026-04-21 — 0.04% —

Full EPSS history (4 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-3644

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
6.0 4.0 MEDIUM
CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:L/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network.
Attack complexity (AC:L)
Exploitation conditions are straightforward and stable.
Attack requirements (AT:P)
Additional preconditions must be present for exploitation.
Privileges required (PR:L)
Low privileges are required.
User interaction (UI:N)
No user interaction is required.
Vulnerable system confidentiality impact (VC:L)
Limited confidentiality impact on the vulnerable system.
Vulnerable system integrity impact (VI:H)
High integrity impact on the vulnerable system.
Vulnerable system availability impact (VA:N)
No availability impact on the vulnerable system.
Subsequent system confidentiality impact (SC:N)
No confidentiality impact on subsequent systems.
Subsequent system integrity impact (SI:N)
No integrity impact on subsequent systems.
Subsequent system availability impact (SA:N)
No availability impact on subsequent systems.
Exploit maturity (threat) (E:X)
Not defined: no reliable threat intelligence; scoring assumes the worst case (equivalent to Attacked).
Confidentiality requirement (CR:X)
Not defined: insufficient information; scoring treats this like High (worst case).
Integrity requirement (IR:X)
Not defined: insufficient information; scoring treats this like High (worst case).
Availability requirement (AR:X)
Not defined: insufficient information; scoring treats this like High (worst case).
Modified attack vector (MAV:X)
Not defined: scoring uses the Base Attack Vector (AV).
Modified attack complexity (MAC:X)
Not defined: scoring uses the Base Attack Complexity (AC).
Modified attack requirements (MAT:X)
Not defined: scoring uses the Base Attack Requirements (AT).
Modified privileges required (MPR:X)
Not defined: scoring uses the Base Privileges Required (PR).
Modified user interaction (MUI:X)
Not defined: scoring uses the Base User Interaction (UI).
Modified vulnerable system confidentiality impact (MVC:X)
Not defined: scoring uses the Base VC metric.
Modified vulnerable system integrity impact (MVI:X)
Not defined: scoring uses the Base VI metric.
Modified vulnerable system availability impact (MVA:X)
Not defined: scoring uses the Base VA metric.
Modified subsequent system confidentiality impact (MSC:X)
Not defined: scoring uses the Base SC metric.
Modified subsequent system integrity impact (MSI:X)
Not defined: scoring uses the Base SI metric.
Modified subsequent system availability impact (MSA:X)
Not defined: scoring uses the Base SA metric.
Safety (supplemental) (S:X)
Not evaluated.
Automatable (supplemental) (AU:X)
Not evaluated.
Recovery (supplemental) (R:X)
Not evaluated.
Value density (supplemental) (V:X)
Not evaluated.
Vulnerability response effort (supplemental) (RE:X)
Not evaluated.
Provider urgency (supplemental) (U:X)
Not evaluated.
 — — [email protected]
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
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:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
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:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:N)
Service keeps running; no real outage angle.
 3.9 3.6 [email protected]

Weakness enumeration for CVE-2026-3644

GitHub Security Advisory for CVE-2026-3644

GHSA-vf33-88pf-hwp3 · Severity: medium — The fix for CVE-2026-0672, which rejected control characters in http.cookies.Morsel, was...

OS Trackers for CVE-2026-3644

vendor priority summary link
debian not yet assigned CVE-2026-3644 not yet assigned priority: Debian including 4 source packages (python3.11, python3.13, python3.14, python3.9), 7 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 4, open 3. https://security-tracker.debian.org/tracker/CVE-2026-3644
redhat medium — https://access.redhat.com/security/cve/CVE-2026-3644
suse medium CVE-2026-3644 severity moderate: SUSE including 220 source package names (2.2.1-7.92:libpython3_11-1_0-3.11.15-slfo.1.1_3.1, 2.2.1-7.92:python311-3.11.15-slfo.1.1_3.1, …), 610 product×package rows across 40 product lines (Container suse/sl-micro/6.0/toolbox, Container suse/sl-micro/6.1/baremetal-os-container, … (40 product lines)): Fixed 337, First Fixed 273. https://www.suse.com/security/cve/CVE-2026-3644/
ubuntu medium CVE-2026-3644 medium priority: Ubuntu including 12 source packages (python2.7, python3.10, …), 60 status rows across 8 suites (bionic, focal, jammy, noble, questing, trusty, upstream, xenial): DNE 30, needs-triage 30. https://ubuntu.com/security/CVE-2026-3644

Affected software / configurations for CVE-2026-3644

Vendor Product Version Raw CPE
python python < 3.13.13 cpe:2.3:a:python:python:*:*:*:*:*:*:*:*
python python >= 3.14.0, < 3.14.4 cpe:2.3:a:python:python:*:*:*:*:*:*:*:*
python python 3.15.0 cpe:2.3:a:python:python:3.15.0:alpha1:*:*:*:*:*:*
python python 3.15.0 cpe:2.3:a:python:python:3.15.0:alpha2:*:*:*:*:*:*
python python 3.15.0 cpe:2.3:a:python:python:3.15.0:alpha3:*:*:*:*:*:*
python python 3.15.0 cpe:2.3:a:python:python:3.15.0:alpha4:*:*:*:*:*:*
python python 3.15.0 cpe:2.3:a:python:python:3.15.0:alpha5:*:*:*:*:*:*
python python 3.15.0 cpe:2.3:a:python:python:3.15.0:alpha6:*:*:*:*:*:*
python python 3.15.0 cpe:2.3:a:python:python:3.15.0:alpha7:*:*:*:*:*:*

References for CVE-2026-3644

cvelogic Threat Intelligence