urllib3 is a widely used Python HTTP library across the ecosystem; this high-severity DoS can crash many client apps and cause widespread disruption.
CVE-2026-97689
urllib3 memory-exhaustion DoS via malformed chunked Transfer-Encoding
Is CVE-2026-97689 being exploited?
Not confirmed. CVE-2026-97689 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked.
How severe is CVE-2026-97689?
CVE-2026-97689 is rated High with a CVSS score of 8.9. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-97689?
Yes. A fix has been recorded for CVE-2026-97689. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-97689 affect?
CVE-2026-97689 affects urllib3 < 2.8.0, Python applications using urllib3 (requests, pip, botocore, homebrew clients). Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-97689?
Upgrade urllib3 to >= 2.8.0 immediately; avoid untrusted servers.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Remote Denial of Service: malicious server sends an unterminated/very long chunk-size line causing unbounded memory allocation and client OOM/crash.
Immediate action required
- affected>= 1.10.3 and < 2.8.0
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.