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Python 3.4-3.14: Email, XML, and Plist Parsing Issues
USN-8018-2
Summary
Some recent Python updates introduced unexpected changes in email, XML, and Plist parsing. This could allow an attacker to inject malicious headers into email messages, cause a denial of service, or make Python use too many resources. You should wait for a new update that fixes these issues or consider downgrading to the previous version until a fix is available.
What to do
- Update canonical python3.4 to version 3.4.3-1ubuntu1~14.04.7+esm20.
- Update canonical python3.5 to version 3.5.2-2ubuntu0~16.04.4~14.04.1+esm10.
- Update canonical python3.5 to version 3.5.2-2ubuntu0~16.04.13+esm22.
- Update canonical python3.6 to version 3.6.9-1~18.04ubuntu1.13+esm9.
- Update canonical python3.7 to version 3.7.5-2ubuntu1~18.04.2+esm10.
- Update canonical python3.8 to version 3.8.0-3ubuntu1~18.04.2+esm10.
- Update canonical python3.8 to version 3.8.10-0ubuntu1~20.04.18+esm6.
- Update canonical python3.9 to version 3.9.5-3ubuntu0~20.04.1+esm10.
- Update canonical python3.10 to version 3.10.12-1~22.04.15.
- Update canonical python3.11 to version 3.11.0~rc1-1~22.04.1~esm9.
- Update canonical python3.12 to version 3.12.3-1ubuntu0.12.
- Update canonical python3.13 to version 3.13.7-1ubuntu0.4.
- Update canonical python3.14 to version 3.14.0-1ubuntu0.3.
Affected software
| Vendor | Product | Affected versions | Fix available |
|---|---|---|---|
| canonical | python3.4 | <= 3.4.3-1ubuntu1~14.04.7+esm20 | 3.4.3-1ubuntu1~14.04.7+esm20 |
| canonical | python3.5 | <= 3.5.2-2ubuntu0~16.04.4~14.04.1+esm10 | 3.5.2-2ubuntu0~16.04.4~14.04.1+esm10 |
| canonical | python3.5 | <= 3.5.2-2ubuntu0~16.04.13+esm22 | 3.5.2-2ubuntu0~16.04.13+esm22 |
| canonical | python3.6 | <= 3.6.9-1~18.04ubuntu1.13+esm9 | 3.6.9-1~18.04ubuntu1.13+esm9 |
| canonical | python3.7 | <= 3.7.5-2ubuntu1~18.04.2+esm10 | 3.7.5-2ubuntu1~18.04.2+esm10 |
| canonical | python3.8 | <= 3.8.0-3ubuntu1~18.04.2+esm10 | 3.8.0-3ubuntu1~18.04.2+esm10 |
| canonical | python3.8 | <= 3.8.10-0ubuntu1~20.04.18+esm6 | 3.8.10-0ubuntu1~20.04.18+esm6 |
| canonical | python3.9 | <= 3.9.5-3ubuntu0~20.04.1+esm10 | 3.9.5-3ubuntu0~20.04.1+esm10 |
| canonical | python3.10 | <= 3.10.12-1~22.04.15 | 3.10.12-1~22.04.15 |
| canonical | python3.11 | <= 3.11.0~rc1-1~22.04.1~esm9 | 3.11.0~rc1-1~22.04.1~esm9 |
| canonical | python3.12 | <= 3.12.3-1ubuntu0.12 | 3.12.3-1ubuntu0.12 |
| canonical | python3.13 | <= 3.13.7-1ubuntu0.4 | 3.13.7-1ubuntu0.4 |
| canonical | python3.14 | <= 3.14.0-1ubuntu0.3 | 3.14.0-1ubuntu0.3 |
Original title
python3.4, python3.5, python3.6, python3.7, python3.8, python3.9,
python3.10, python3.11, python3.12, python3.13, python3.14 regression
Original description
USN-8018-1 fixed vulnerabilities in python3. That update introduced
regressions. The patches for CVE-2025-15366 and CVE-2025-15367 caused
behavior regressions in IMAP and POP3 handling, which upstream chose to
avoid by not backporting them. Additionally, the patch for CVE-2026-0865
incorrectly rejected horizontal tabs in wsgiref headers. This update fixes
these problems.
We apologize for the inconvenience.
Original advisory details:
Denis Ledoux discovered that Python incorrectly parsed email message
headers. An attacker could possibly use this issue to inject arbitrary
headers into email messages. This issue only affected python3.6,
python3.7, python3.8, python3.9, python3.10, python3.11, python3.12,
python3.13, and python3.14 packages. (CVE-2025-11468)
Jacob Walls, Shai Berger, and Natalia Bidart discovered that Python
inefficiently parsed XML input with quadratic complexity. An attacker
could possibly use this issue to cause a denial of service.
(CVE-2025-12084)
It was discovered that Python incorrectly parsed malicious plist files. An
attacker could possibly use this issue to cause Python to use excessive
resources, leading to a denial of service. This issue only affected
python3.5, python3.6, python3.7, python3.8, python3.9, python3.10,
python3.11, python3.12, python3.13, and python3.14 packages.
(CVE-2025-13837)
Omar Hasan discovered that Python incorrectly parsed URL mediatypes. An
attacker could possibly use this issue to inject arbitrary HTTP headers.
(CVE-2025-15282)
Omar Hasan discovered that Python incorrectly parsed malicious IMAP
inputs. An attacker could possibly use this issue to inject arbitrary
IMAP commands. (CVE-2025-15366)
Omar Hasan discovered that Python incorrectly parsed malicious POP3
inputs. An attacker could possibly use this issue to inject arbitrary
POP3 commands. (CVE-2025-15367)
Omar Hasan discovered that Python incorrectly parsed malicious HTTP cookie
headers. An attacker could possibly use this issue to inject arbitrary
HTTP headers. (CVE-2026-0672)
Omar Hasan discovered that Python incorrectly parsed malicious HTTP header
names and values. An attacker could possibly use this issue to inject
arbitrary HTTP headers. (CVE-2026-0865)
regressions. The patches for CVE-2025-15366 and CVE-2025-15367 caused
behavior regressions in IMAP and POP3 handling, which upstream chose to
avoid by not backporting them. Additionally, the patch for CVE-2026-0865
incorrectly rejected horizontal tabs in wsgiref headers. This update fixes
these problems.
We apologize for the inconvenience.
Original advisory details:
Denis Ledoux discovered that Python incorrectly parsed email message
headers. An attacker could possibly use this issue to inject arbitrary
headers into email messages. This issue only affected python3.6,
python3.7, python3.8, python3.9, python3.10, python3.11, python3.12,
python3.13, and python3.14 packages. (CVE-2025-11468)
Jacob Walls, Shai Berger, and Natalia Bidart discovered that Python
inefficiently parsed XML input with quadratic complexity. An attacker
could possibly use this issue to cause a denial of service.
(CVE-2025-12084)
It was discovered that Python incorrectly parsed malicious plist files. An
attacker could possibly use this issue to cause Python to use excessive
resources, leading to a denial of service. This issue only affected
python3.5, python3.6, python3.7, python3.8, python3.9, python3.10,
python3.11, python3.12, python3.13, and python3.14 packages.
(CVE-2025-13837)
Omar Hasan discovered that Python incorrectly parsed URL mediatypes. An
attacker could possibly use this issue to inject arbitrary HTTP headers.
(CVE-2025-15282)
Omar Hasan discovered that Python incorrectly parsed malicious IMAP
inputs. An attacker could possibly use this issue to inject arbitrary
IMAP commands. (CVE-2025-15366)
Omar Hasan discovered that Python incorrectly parsed malicious POP3
inputs. An attacker could possibly use this issue to inject arbitrary
POP3 commands. (CVE-2025-15367)
Omar Hasan discovered that Python incorrectly parsed malicious HTTP cookie
headers. An attacker could possibly use this issue to inject arbitrary
HTTP headers. (CVE-2026-0672)
Omar Hasan discovered that Python incorrectly parsed malicious HTTP header
names and values. An attacker could possibly use this issue to inject
arbitrary HTTP headers. (CVE-2026-0865)
- https://ubuntu.com/security/notices/USN-8018-2 Vendor Advisory
- https://ubuntu.com/security/CVE-2025-15366 Third Party Advisory
- https://ubuntu.com/security/CVE-2025-15367 Third Party Advisory
- https://ubuntu.com/security/CVE-2026-0865 Third Party Advisory
- https://bugs.launchpad.net/bugs/2143706 Third Party Advisory
Published: 9 Mar 2026 · Updated: 13 Mar 2026 · First seen: 10 Mar 2026