How severe is CVE-2026-15308?

CVE-2026-15308 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 none, and availability high.

Is CVE-2026-15308 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (48th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-15308?

CVE-2026-15308 primarily affects Python. In total, 12 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2026-15308?

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-2026-15308 published?

CVE-2026-15308 was published on 2026-07-09 and last updated on 2026-08-20.

CVE-2026-15308

CVE-2026-15308 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-400.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v4: 8.7
EPSS exploit prediction: 1% (48th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-400
Affected product: Python
Published: 2026-07-09
Last modified: 2026-08-20

Description

The incremental HTML parser (html.parser.HTMLParser) allows for CPU denial-of-service through repeated unterminated markup declarations when processing uncontrolled data.

Frequently asked questions

What is CVE-2026-15308?: The incremental HTML parser (html.parser.HTMLParser) allows for CPU denial-of-service through repeated unterminated markup declarations when processing uncontrolled data.
How severe is CVE-2026-15308?: CVE-2026-15308 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 none, and availability high.
Is CVE-2026-15308 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (48th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-15308?: CVE-2026-15308 primarily affects Python. In total, 12 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2026-15308?: 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-2026-15308 published?: CVE-2026-15308 was published on 2026-07-09 and last updated on 2026-08-20.

References

Affected products (12)

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:*:*:*:*:*:*
cpe:2.3:a:python:python:3.15.0:alpha8:*:*:*:*:*:*
cpe:2.3:a:python:python:3.15.0:beta1:*:*:*:*:*:*
cpe:2.3:a:python:python:3.15.0:beta2:*:*:*:*:*:*
cpe:2.3:a:python:python:3.15.0:beta3:*:*:*:*:*:*

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Threat intelligence

Threat-intel indicators referencing this CVE:

45.194.120.252 (ipv4-addr)
64.227.116.82 (ipv4-addr)
141.253.107.23 (ipv4-addr)
143.244.159.156 (ipv4-addr)
202.188.47.41 (ipv4-addr)
202.10.36.104 (ipv4-addr)
187.62.205.20 (ipv4-addr)
125.22.162.46 (ipv4-addr)