CVE-2026-15308
Python html.parser allows CPU DoS via unterminated markup.
Is CVE-2026-15308 being exploited?
Not confirmed. CVE-2026-15308 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. EPSS currently estimates a 0.64% probability of exploitation in the next 30 days.
How severe is CVE-2026-15308?
CVE-2026-15308 is rated High with a CVSS score of 8.7. 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-2026-15308?
Yes. A fix has been recorded for CVE-2026-15308. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-15308 affect?
CVE-2026-15308 affects Python standard library: html.parser.HTMLParser, Applications using Python's html.parser, Web services that parse untrusted HTML. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-15308?
Apply vendor patch when released; sanitize/limit HTML input; enforce parsing timeouts
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Remote CPU exhaustion and service disruption by feeding crafted/unterminated HTML to Python's html.parser (denial-of-service).
Patch when possible
- affected< 3.10.21
- affected>= 3.11.0 and < 3.11.16
- affected>= 3.12.0 and < 3.12.14
- affected>= 3.13.0 and < 3.13.15
- affected>= 3.14.0 and < 3.14.7
- affected>= 3.15.0a1 and < 3.15.0b4
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.