CVE-2026-0865
published 2026-01-20CVE-2026-0865: User-controlled header names and values containing newlines can allow injecting HTTP headers.
PriorityP431medium5.9CVSS 4.0
AVNACLATPPRHUINVCNVIHVANSCNSINSANEXCRXIRXARXMAVXMACXMATXMPRXMUIXMVCXMVIXMVAXMSCXMSIXMSAXSXAUXRXVXREXUX
EPSS
0.46%
37.2th percentile
User-controlled header names and values containing newlines can allow injecting HTTP headers.
Affected
13 ranges
| Vendor | Product | Version range | Fixed in |
|---|---|---|---|
| debian | jython | < python3.13 3.13.12-1 (forky) | python3.13 3.13.12-1 (forky) |
| debian | pypy3 | < python3.13 3.13.12-1 (forky) | python3.13 3.13.12-1 (forky) |
| debian | python2.7 | < python3.13 3.13.12-1 (forky) | python3.13 3.13.12-1 (forky) |
| debian | python3.11 | < python3.13 3.13.12-1 (forky) | python3.13 3.13.12-1 (forky) |
| debian | python3.13 | < python3.13 3.13.12-1 (forky) | python3.13 3.13.12-1 (forky) |
| debian | python3.14 | < python3.13 3.13.12-1 (forky) | python3.13 3.13.12-1 (forky) |
| debian | python3.9 | < python3.13 3.13.12-1 (forky) | python3.13 3.13.12-1 (forky) |
| python_software_foundation | cpython | < 3.10.20 | 3.10.20 |
| python_software_foundation | cpython | >= 3.11.0 < 3.11.15 | 3.11.15 |
| python_software_foundation | cpython | >= 3.12.0 < 3.12.13 | 3.12.13 |
| python_software_foundation | cpython | >= 3.13.0 < 3.13.12 | 3.13.12 |
| python_software_foundation | cpython | >= 3.14.0 < 3.14.3 | 3.14.3 |
| python_software_foundation | cpython | >= 3.15.0a1 < 3.15.0a6 | 3.15.0a6 |
CVSS provenance
nvdv4.05.9MEDIUMCVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
osv5.9MEDIUM
vendor_debian5.9MEDIUM
vendor_redhat5.9MEDIUM
vendor_ubuntu5.3MEDIUM
Stop checking back — get the weekly exploitation signal.
Every Monday: what got weaponized or added to CISA KEV in the last seven days — each CVE cross-linked to its PoC, Nuclei template, and detection rule. Free, one email a week, unsubscribe in one click.
OSV
python2.7 vulnerabilities
osv·2026-03-19·CVSS 5.7
CVE-2025-12084 [MEDIUM] python2.7 vulnerabilities
python2.7 vulnerabilities
USN-8018-1 fixed CVE-2025-12084, CVE-2025-15282, CVE-2026-0672,
CVE-2026-0865 for python3. This update provides the corresponding updates
for python2.7.
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 pars
OSV
python3.4, python3.5, python3.6, python3.7, python3.8, python3.9,
python3.10, python3.11, python3.12, python3.13, python3.14 regression
osv·2026-03-09·CVSS 5.7
CVE-2025-15366 [MEDIUM] python3.4, python3.5, python3.6, python3.7, python3.8, python3.9,
python3.10, python3.11, python3.12, python3.13, python3.14 regression
python3.4, python3.5, python3.6, python3.7, python3.8, python3.9,
python3.10, python3.11, python3.12, python3.13, python3.14 regression
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
OSV
python3.14, python3.13, python3.12, python3.11, python3.10, python3.9,
python3.8, python3.7, python3.6, python3.5, python3.4 vulnerabilities
osv·2026-02-05·CVSS 5.7
CVE-2025-11468 [MEDIUM] python3.14, python3.13, python3.12, python3.11, python3.10, python3.9,
python3.8, python3.7, python3.6, python3.5, python3.4 vulnerabilities
python3.14, python3.13, python3.12, python3.11, python3.10, python3.9,
python3.8, python3.7, python3.6, python3.5, python3.4 vulnerabilities
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
GHSA
GHSA-5mc7-p6pj-r3f5: User-controlled header names and values containing newlines can allow injecting HTTP headers
ghsa_unreviewed·2026-01-21
CVE-2026-0865 [MEDIUM] CWE-74 GHSA-5mc7-p6pj-r3f5: User-controlled header names and values containing newlines can allow injecting HTTP headers
User-controlled header names and values containing newlines can allow injecting HTTP headers.
OSV
CVE-2026-0865: User-controlled header names and values containing newlines can allow injecting HTTP headers
osv·2026-01-20·CVSS 5.9
CVE-2026-0865 [MEDIUM] CVE-2026-0865: User-controlled header names and values containing newlines can allow injecting HTTP headers
User-controlled header names and values containing newlines can allow injecting HTTP headers.
Ubuntu
Python 2.7 vulnerabilities
vendor_ubuntu·2026-03-19·CVSS 5.3
CVE-2025-12084 [MEDIUM] Python 2.7 vulnerabilities
Title: Python 2.7 vulnerabilities
Summary: Several security issues were fixed in python2.7
USN-8018-1 fixed CVE-2025-12084, CVE-2025-15282, CVE-2026-0672,
CVE-2026-0865 for python3. This update provides the corresponding updates
for python2.7.
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
Ubuntu
Python regression
vendor_ubuntu·2026-03-09·CVSS 5.3
CVE-2025-15367 [MEDIUM] Python regression
Title: Python regression
Summary: USN-8018-1 introduced a regression in Python
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,
pytho
Ubuntu
Python vulnerabilities
vendor_ubuntu·2026-02-05·CVSS 5.3
CVE-2025-15366 [MEDIUM] Python vulnerabilities
Title: Python vulnerabilities
Summary: Several security issues were fixed in Python.
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
Red Hat
cpython: wsgiref.headers.Headers allows header newline injection in Python
vendor_redhat·2026-01-20·CVSS 5.9
CVE-2026-0865 [MEDIUM] CWE-74 cpython: wsgiref.headers.Headers allows header newline injection in Python
cpython: wsgiref.headers.Headers allows header newline injection in Python
User-controlled header names and values containing newlines can allow injecting HTTP headers.
Missing newline filtering has been discovered in Python. User-controlled header names and values containing newlines can allow injecting HTTP headers.
Mitigation: Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.
Package: firefox (Red Hat Enterprise Linux 10) - Fix deferred
Package: python3.14 (Red Hat Enterprise Linux 10) - Fix deferred
Package: python (Red Hat Enterprise Linux 6) - Fix deferred
Package: firefox (Red Hat Enterprise Lin
Debian
CVE-2026-0865: jython - User-controlled header names and values containing newlines can allow injecting ...
vendor_debian·2026·CVSS 5.9
CVE-2026-0865 [MEDIUM] CVE-2026-0865: jython - User-controlled header names and values containing newlines can allow injecting ...
User-controlled header names and values containing newlines can allow injecting HTTP headers.
Scope: local
bookworm: open
bullseye: open
forky: open
sid: open
trixie: open
No detection rules found.
No public exploits indexed.
Bugzilla
CVE-2026-0865 asahi-installer: wsgiref.headers.Headers allows header newline injection in Python [fedora-42]
bugzilla·2026-01-21·CVSS 5.9
CVE-2026-0865 [MEDIUM] CVE-2026-0865 asahi-installer: wsgiref.headers.Headers allows header newline injection in Python [fedora-42]
CVE-2026-0865 asahi-installer: wsgiref.headers.Headers allows header newline injection in Python [fedora-42]
Disclaimer: Community trackers are created by Red Hat Product Security team on a best effort basis. Package maintainers are required to ascertain if the flaw indeed affects their package, before starting the update process.
Discussion:
This message is a reminder that Fedora Linux 42 is nearing its end of life.
Fedora will stop maintaining and issuing updates for Fedora Linux 42 on 2026-05-13.
It is Fedora's policy to close all bug reports from releases that are no longer
maintained. At that time this bug will be closed as EOL if it remains open with a
'version' of '42'.
Package Maintainer: If you wish for this bug to remain open because you
plan to fix it in a currently maintain
Bugzilla
CVE-2026-0865 cpython: wsgiref.headers.Headers allows header newline injection in Python
bugzilla·2026-01-20·CVSS 5.9
CVE-2026-0865 [MEDIUM] CVE-2026-0865 cpython: wsgiref.headers.Headers allows header newline injection in Python
CVE-2026-0865 cpython: wsgiref.headers.Headers allows header newline injection in Python
User-controlled header names and values containing newlines can allow injecting HTTP headers.
Discussion:
This issue has been addressed in the following products:
Red Hat Enterprise Linux 8
Via RHSA-2026:2128 https://access.redhat.com/errata/RHSA-2026:2128
---
This issue has been addressed in the following products:
Red Hat Enterprise Linux 8
Via RHSA-2026:4463 https://access.redhat.com/errata/RHSA-2026:4463
---
This issue has been addressed in the following products:
Red Hat Enterprise Linux 8
Via RHSA-2026:4473 https://access.redhat.com/errata/RHSA-2026:4473
---
This issue has been addressed in the following products:
Red Hat Enterprise Linux 10
Via RHSA-2026:4713 https://access.redh
Wiz
CVE-2026-0865 Impact, Exploitability, and Mitigation Steps | Wiz
blogs_wiz·CVSS 5.9
CVE-2026-0865 [MEDIUM] CVE-2026-0865 Impact, Exploitability, and Mitigation Steps | Wiz
## CVE-2026-0865 :
Rocky Linux vulnerability analysis and mitigation
User-controlled header names and values containing newlines can allow injecting HTTP headers.
Source : NVD
## 5.9
Score
Published January 20, 2026
Severity MEDIUM
CNA Score 5.9
Affected Technologies
Rocky Linux
Python Interpreter
Has Public Exploit No
Has CISA KEV Exploit No
CISA KEV Release Date N/A
CISA KEV Due Date N/A
Exploitation Probability Percentile (EPSS) 32.7
Exploitation Probability (EPSS) 0.1
Affected packages and libraries
python3.15-freethreading-libs
python313-nogil
Sources
NVD
AlmaLinux 8 Severity MEDIUM Has Fix Added at: Feb 08, 2026
AlmaLinux 9 Severity MEDIUM Has Fix Added at: Mar 13, 2026
CBL-Mariner 2.0 Severity MEDIUM Has Fix Added at: Mar 10, 2026
CBL-Mariner 3.0 Severity
https://github.com/python/cpython/commit/22e4d55285cee52bc4dbe061324e5f30bd4dee58https://github.com/python/cpython/commit/23e3c0ae867cca0130e441e776c9955b9027c510https://github.com/python/cpython/commit/286e3ac39984fe85a17f4ab39c64d382137aae5fhttps://github.com/python/cpython/commit/2f840249550e082dc351743f474ba56da10478d2https://github.com/python/cpython/commit/4802b96a2cde58570c24c13ef3289490980961c5https://github.com/python/cpython/commit/66da7bf6fe7b81e3ecc9c0a25bd47d4616c8d1a6https://github.com/python/cpython/commit/83ecd18779f286d872f68bfce175651e407d9fffhttps://github.com/python/cpython/commit/8bb044d29310bb05d15086cdaa8bf64867d61a97https://github.com/python/cpython/commit/bfba660085767f8c2d582134e9d511a85eda04cfhttps://github.com/python/cpython/commit/c592227ffb48679af9845a45dbb0875d975bb219https://github.com/python/cpython/commit/e4846a93ac07a8ae9aa18203af0dd13d6e7a6995https://github.com/python/cpython/commit/f7fceed79ca1bceae8dbe5ba5bc8928564da7211https://github.com/python/cpython/issues/143916https://github.com/python/cpython/pull/143917https://mail.python.org/archives/list/[email protected]/thread/BJ6QPHNSHJTS3A7CFV6IBMCAP2DWRVNT/
2026-01-20
Published