CVE-2021-3737 — A flaw was found in python. An improperly handled HTTP response in the HTTP client code of python...

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

• Documented patch — bugzilla.redhat.com (NIST National Vulnerability Database)
• Documented patch — github.com (NIST National Vulnerability Database)
• Documented patch — github.com (NIST National Vulnerability Database)
• Documented patch — python-security.readthedocs.io (NIST National Vulnerability Database)
• Documented patch — ubuntu.com (NIST National Vulnerability Database)
• Documented patch — www.oracle.com (NIST National Vulnerability Database)

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

1. Identify exposed assets running the affected vendor/product/version combinations (Canonical Ubuntu Linux, Fedoraproject Fedora, Netapp Hci…).
2. The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
3. Apply the fixed version or the patch documented under Remediation.
4. EPSS ahead of 96% of scored CVEs: prioritize it in the patch queue.
5. Search available logs for exploit probes matching the vulnerability class (denial of service), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-400 · Uncontrolled Resource Consumption

Other CVEs with this weakness →

EPSS over time FIRST

Oct 13, 2026 → Oct 16, 2026 · 4 reading(s) · max 13.17%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

• Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
• Track CPU/memory spikes and availability drops correlated with request patterns.

Timeline

What happened to this CVE, newest first.

• 2026
• SSVC assessment updated
  Oct 14, 2026 · CVE Program (cve.org) e CISA ADP
• Record published
  Oct 14, 2026
• Fix documented
  Oct 14, 2026 · NIST National Vulnerability Database
• Affected products added · python/python, redhat/codeready linux builder, redhat/codeready linux builder for ibm z systems, redhat/codeready linux
  Oct 14, 2026 · NIST National Vulnerability Database
• CVSS changed · 7.5
  Oct 14, 2026 · NIST National Vulnerability Database
• Source status changed · → Modified
  Oct 14, 2026 · NIST National Vulnerability Database
• Record created in this database
  Oct 14, 2026 · Alertas do Telegram
• 2022
• CVE published
  Mar 4, 2022 · redhat

Source activity

Repeated readings are counted rather than listed.

• 2× References added · Oct 14, 2026 – Oct 14, 2026
• 1× Official description updated · Oct 14, 2026 – Oct 14, 2026

References

17 on the record

• bugs.python.org/issue44022
  Exploit, Issue Tracking, Vendor Advisory, NIST National Vulnerability Database
• github.com/python/cpython/pull/26503
  Patch, Third Party Advisory, NIST National Vulnerability Database
• bugzilla.redhat.com/show_bug.cgi
  Issue Tracking, Patch, Third Party Advisory, NIST National Vulnerability Database
• github.com/python/cpython/pull/25916
  Patch, Third Party Advisory, NIST National Vulnerability Database
• www.oracle.com/security-alerts/cpujul2022.html
  Patch, Third Party Advisory, NIST National Vulnerability Database
• python-security.readthedocs.io/vuln/urllib-100-continue-loop.html
  Patch, Third Party Advisory, NIST National Vulnerability Database
• ubuntu.com/security/CVE-2021-3737
  Patch, Third Party Advisory, NIST National Vulnerability Database
• nvd.nist.gov/vuln/detail/CVE-2021-3737
  GitHub Security Advisories
• lists.debian.org/debian-lts-announce/2024/11/msg00024.html
  NIST National Vulnerability Database
• lists.debian.org/debian-lts-announce/2023/06/msg00039.html
  mailing-list, NIST National Vulnerability Database
• github.com/python/cpython/commit/ea9327036680acc92d9f89eaf6f6a54d2f8d78d9
  GitHub Security Advisories
• lists.debian.org/debian-lts-announce/2023/05/msg00024.html
  mailing-list, NIST National Vulnerability Database
• lists.debian.org/debian-lts-announce/2024/12/msg00000.html
  NIST National Vulnerability Database
• cert-portal.siemens.com/productcert/html/ssa-398330.html
  NIST National Vulnerability Database
• security.netapp.com/advisory/ntap-20220407-0009/
  Third Party Advisory, NIST National Vulnerability Database
• github.com/advisories/GHSA-hr7v-m862-8hh8
  GitHub Security Advisories
• security.netapp.com/advisory/ntap-20220407-0009
  GitHub Security Advisories

Elsewhere on this site

Related CVEs (same products)

• Medium CVE-2026-104046 Sssd: sssd: denial of service via incomplete identity provider authentication requests 10d
• Medium CVE-2026-104045 Sssd: sssd: denial of service via race condition in autofs responder 10d
• Medium CVE-2026-104047 Sssd: sssd: information disclosure via query injection in entra id lookups 10d
• High CVE-2026-104048 Sssd: sssd: authorization bypass via cross-domain username collision in hbac evaluation 10d
• Medium CVE-2026-104040 Sssd: sssd: information disclosure via odata injection in entra id lookups 11d
• High CVE-2026-102558 Libsoup: libsoup: heap buffer overflow during websocket receive-buffer growth 17d

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

• No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
• No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
• No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2021-3737 is "A flaw was found in python. An improperly handled HTTP response in the HTTP client code of python...", rated High. It affects Ubuntu Linux (Canonical); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 7.5 describes technical severity. EPSS 13.17% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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