Several Debian LTS advisories were released covering vulnerabilities in the web application firewall ModSecurity, the ASN.1 library pyasn1, and the asynchronous web framework Tornado. The modsecurity‑apache update addresses CVE-2025-54571 by preventing attackers from overriding HTTP response Content-Type headers, while the pyasn1 updates fix a denial‑of‑service flaw that can exhaust memory when parsing malformed OID/RELATIVE-OID values (CVE-2026-23490). The python-tornado advisories cover three CVEs, CVE-2025-67724, CVE-2025-67725, and CVE-2025-67726, which expose issues such as XSS, header injection, and quadratic performance attacks that can lead to denial of service. All affected packages have been upgraded to patched versions, and users are urged to install the latest releases promptly.

Debian GNU/Linux 9 (Stretch) Extended LTS:
ELA-1633-1 modsecurity-apache security update

Debian GNU/Linux 9 (Stretch) and 10 (Buster) Extended LTS:
ELA-1634-1 pyasn1 security update

Debian GNU/Linux 10 (Buster) Extended LTS:
ELA-1635-1 python-tornado security update

Debian GNU/Linux 11 (Bullseye) LTS:
[DLA 4463-1] pyasn1 security update

ELA-1633-1 modsecurity-apache security update

Package : modsecurity-apache
Version : 2.9.1-2+deb9u5 (stretch)

Related CVEs :
CVE-2025-54571

ModSecurity is an open source, cross platform web application firewall (WAF)
engine for Apache, IIS and Nginx. In versions 2.9.11 and below, an attacker
can override the HTTP response’s Content-Type, which could lead to several
issues depending on the HTTP scenario.

ELA-1633-1 modsecurity-apache security update

[SECURITY] [DLA 4463-1] pyasn1 security update

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Debian LTS Advisory DLA-4463-1 debian-lts@lists.debian.org
https://www.debian.org/lts/security/ Utkarsh Gupta
February 01, 2026 https://wiki.debian.org/LTS
- -----------------------------------------------------------------------

Package : pyasn1
Version : 0.4.8-1+deb11u1
CVE ID : CVE-2026-23490
Debian Bug : 1125753

It was discovered that pyasn1, a generic ASN.1 library for Python, is
prone to a denial of service vulnerability, which may result in memory
exhaustion from malformed OID/RELATIVE-OID with excessive continuation
octets.

For Debian 11 bullseye, this problem has been fixed in version
0.4.8-1+deb11u1.

We recommend that you upgrade your pyasn1 packages.

For the detailed security status of pyasn1 please refer to
its security tracker page at:
https://security-tracker.debian.org/tracker/pyasn1

Further information about Debian LTS security advisories, how to apply
these updates to your system and frequently asked questions can be
found at: https://wiki.debian.org/LTS

ELA-1634-1 pyasn1 security update

Package : pyasn1
Version : 0.1.9-2+deb9u1 (stretch), 0.4.2-3+deb10u1 (buster)

Related CVEs :
CVE-2026-23490

It was discovered that pyasn1, a generic ASN.1 library for Python, is
prone to a denial of service vulnerability, which may result in memory
exhaustion from malformed OID/RELATIVE-OID with excessive continuation
octets.

ELA-1634-1 pyasn1 security update

ELA-1635-1 python-tornado security update

Package : python-tornado
Version : 5.1.1-4+deb10u3 (buster)

Related CVEs :
CVE-2025-67724
CVE-2025-67725
CVE-2025-67726

Multiple vulnerabilities were discovered in python-tornado, a scalable,
non-blocking Python web framework and asynchronous networking library.

CVE-2025-67724
Custom reason phrases can cause multiple vulnerabilities (like XSS,
header injection, ...) due to being used unescaped in HTTP headers.

CVE-2025-67725
A single maliciously crafted HTTP request can cause a possible DoS
due to quadratic performance of repeated header lines.

CVE-2025-67726
An inefficient algorithm when parsing parameters for HTTP header
values can potentially cause a DoS.

ELA-1635-1 python-tornado security update