CVE-2020-26116

CVE-2020-26116 is a high-severity vulnerability in Python with a CVSS 3.x base score of 7.2. 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-74.

Key facts

• Severity: High (CVSS 3.x base score 7.2)
• CVSS v2: 6.4
• EPSS exploit prediction: 6% (93rd percentile)
• Actively exploited: Not listed in CISA KEV
• Weakness: CWE-74
• Affected product: Python
• Published: 2020-09-27
• Last modified: 2026-06-17

Description

http.client in Python 3.x before 3.5.10, 3.6.x before 3.6.12, 3.7.x before 3.7.9, and 3.8.x before 3.8.5 allows CRLF injection if the attacker controls the HTTP request method, as demonstrated by inserting CR and LF control characters in the first argument of HTTPConnection.request.

Frequently asked questions

What is CVE-2020-26116?

http.client in Python 3.x before 3.5.10, 3.6.x before 3.6.12, 3.7.x before 3.7.9, and 3.8.x before 3.8.5 allows CRLF injection if the attacker controls the HTTP request method, as demonstrated by inserting CR and LF control characters in the first argument of HTTPConnection.request.

How severe is CVE-2020-26116?

CVE-2020-26116 has a CVSS 3.x base score of 7.2, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity low, and availability none.

Is CVE-2020-26116 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 6% (93rd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2020-26116?

CVE-2020-26116 primarily affects Python. In total, 13 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2020-26116?

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.

When was CVE-2020-26116 published?

CVE-2020-26116 was published on 2020-09-27 and last updated on 2026-06-17.

References

• http://lists.opensuse.org/opensuse-security-announce/2020-11/msg00027.html
• https://bugs.python.org/issue39603
• https://lists.debian.org/debian-lts-announce/2020/11/msg00032.html
• https://lists.debian.org/debian-lts-announce/2023/05/msg00024.html
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/BW4GCLQISJCOEGQNIMVUZDQMIY6RR6CC/
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/HDQ2THWU4GPV4Y5H5WW5PFMSWXL2CRFD/
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/JWMAVY4T4257AZHTF2RZJKNJNSJFY24O/
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/OXI72HIHMXCQFWTULUXDG7VDA2BCYL4Y/
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QOX7DGMMWWL6POCRYGAUCISOLR2IG3XV/
• https://python-security.readthedocs.io/vuln/http-header-injection-method.html
• https://security.gentoo.org/glsa/202101-18
• https://security.netapp.com/advisory/ntap-20201023-0001/
• https://usn.ubuntu.com/4581-1/
• https://www.oracle.com/security-alerts/cpuoct2021.html

Affected products (13)

• cpe:2.3:a:python:python:*:*:*:*:*:*:*:*
• cpe:2.3:o:fedoraproject:fedora:31:*:*:*:*:*:*:*
• cpe:2.3:o:fedoraproject:fedora:32:*:*:*:*:*:*:*
• cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:*
• cpe:2.3:o:canonical:ubuntu_linux:12.04:*:*:*:-:*:*:*
• cpe:2.3:o:canonical:ubuntu_linux:14.04:*:*:*:esm:*:*:*
• cpe:2.3:o:canonical:ubuntu_linux:16.04:*:*:*:esm:*:*:*
• cpe:2.3:o:canonical:ubuntu_linux:18.04:*:*:*:lts:*:*:*
• cpe:2.3:a:netapp:solidfire:-:*:*:*:*:*:*:*
• cpe:2.3:h:netapp:hci_storage_node:-:*:*:*:*:*:*:*
• cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:*
• cpe:2.3:a:oracle:zfs_storage_appliance_kit:8.8:*:*:*:*:*:*:*
• cpe:2.3:o:opensuse:leap:15.1:*:*:*:*:*:*:*

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Threat intelligence

Threat-intel indicators referencing this CVE:

• 120.28.109.188 (ipv4-addr)
• 222.88.237.152 (ipv4-addr)
• 120.224.15.67 (ipv4-addr)
• 141.109.168.51 (ipv4-addr)
• 103.129.59.62 (ipv4-addr)
• 175.6.181.236 (ipv4-addr)
• 202.188.47.41 (ipv4-addr)
• 8.213.129.95 (ipv4-addr)