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CVE-2026-15308VulnerabilityPublished Updated

Red Hat Security Advisory: python3 security update

Affects Red Hat python3Source GCVE Database

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Authoritative record:CVE-2026-15308· High 8.7

Not known to be exploited · CVSS 8.7 High · fixed in Red Hat package updates : patch Red Hat CPython soon.

Data as of 1 Nov 2026, 01:55 UTC

CVSS 4.0 base score
8.7High
How severe the flaw is on the 0–10 CVSS scale.
Patch
Available – fixed in 3.15.0b4, 3.14.7, 3.13.15 +3
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 9 Jul 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 31 Oct 2026.

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

ProductAffectedFixed in
Python Software FoundationCPythonAffected
  • >=3.15.0a1 <3.15.0b4
Fixed in
  • 3.15.0b4
Python Software FoundationCPythonAffected
  • >=3.14.0 <3.14.7
Fixed in
  • 3.14.7
Python Software FoundationCPythonAffected
  • >=3.13.0 <3.13.15
Fixed in
  • 3.13.15
Python Software FoundationCPythonAffected
  • >=3.12.0 <3.12.14
Fixed in
  • 3.12.14
Python Software FoundationCPythonAffected
  • >=3.11.0 <3.11.16
Fixed in
  • 3.11.16
Python Software FoundationCPythonAffected
  • <3.10.21
Fixed in
  • 3.10.21

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Red Hat has released an updated python3 package that fixes this vulnerability. Users of Red Hat Enterprise Linux 8.4 should apply the security update as described in the Red Hat advisory RHSA-2026:50816. Refer to https://access.redhat.com/articles/11258 for update instructions. No additional mitigation is required beyond applying the official patch.

Description

A denial of service vulnerability (CVE-2026-15308) exists in the Python HTML parser due to repeated unterminated markup declarations. This flaw could allow an attacker to cause excessive CPU usage, leading to a denial of service condition. Red Hat has issued a security update addressing this issue in python3 packages for Red Hat Enterprise Linux 8.4. The update is rated as Important by Red Hat Product Security. No public exploit code or in-the-wild exploitation has been reported.

References

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