CVE-2026-3644

CVE-2026-3644 is a high-severity vulnerability in Python with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-20.

Key facts

• Severity: High (CVSS 3.x base score 7.5)
• CVSS v4: 6.0
• EPSS exploit prediction: 0% (34th percentile)
• Actively exploited: Not listed in CISA KEV
• EU (EUVD) id: EUVD-2026-12484
• Weakness: CWE-20
• Affected product: Python
• Published: 2026-03-16
• Last modified: 2026-06-30

Description

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().

Frequently asked questions

What is CVE-2026-3644?

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().

How severe is CVE-2026-3644?

CVE-2026-3644 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability none.

Is CVE-2026-3644 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (34th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-3644?

CVE-2026-3644 primarily affects Python. In total, 8 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2026-3644?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

Does CVE-2026-3644 have an EU (EUVD) identifier?

Yes. CVE-2026-3644 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-12484.

When was CVE-2026-3644 published?

CVE-2026-3644 was published on 2026-03-16 and last updated on 2026-06-30.

References

• https://github.com/python/cpython/commit/556aa098e738b127c714866f819b4abe2f7593d8
• https://github.com/python/cpython/commit/57e88c1cf95e1481b94ae57abe1010469d47a6b4
• https://github.com/python/cpython/commit/62ceb396fcbe69da1ded3702de586f4072b590dd
• https://github.com/python/cpython/commit/d16ecc6c3626f0e2cc8f08c309c83934e8a979dd
• https://github.com/python/cpython/commit/dae4b1a21f8df4570e30986affd61bbe4ade4cef
• https://github.com/python/cpython/issues/145599
• https://github.com/python/cpython/pull/145600
• https://mail.python.org/archives/list/[email protected]/thread/H6CADMBCDRFGWCMOXWUIHFJNV43GABJ7/

Affected products (8)

• cpe:2.3:a:python:python:*:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:3.15.0:alpha1:*:*:*:*:*:*
• cpe:2.3:a:python:python:3.15.0:alpha2:*:*:*:*:*:*
• cpe:2.3:a:python:python:3.15.0:alpha3:*:*:*:*:*:*
• cpe:2.3:a:python:python:3.15.0:alpha4:*:*:*:*:*:*
• cpe:2.3:a:python:python:3.15.0:alpha5:*:*:*:*:*:*
• cpe:2.3:a:python:python:3.15.0:alpha6:*:*:*:*:*:*
• cpe:2.3:a:python:python:3.15.0:alpha7:*:*:*:*:*:*

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Threat intelligence

Threat-intel indicators referencing this CVE:

• 41.63.62.103 (ipv4-addr)
• 203.192.232.180 (ipv4-addr)
• 149.86.233.213 (ipv4-addr)
• 141.109.168.26 (ipv4-addr)
• 141.109.168.107 (ipv4-addr)
• 125.212.235.194 (ipv4-addr)
• 120.28.109.188 (ipv4-addr)
• 103.61.123.132 (ipv4-addr)