Recent Debian security advisories address critical vulnerabilities across several widely used software packages. Perl requires an update because thread creation can temporarily shift the current directory, potentially allowing local attackers to access restricted files or inject malicious code. PostgreSQL versions 11 and 9.6 received follow-up patches to fix a regression in multibyte character handling while also incorporating minor upstream improvements. Meanwhile, MapServer and MuPDF both address heap buffer overflow flaws that could otherwise enable remote denial of service attacks or arbitrary code execution through crafted inputs.

ELA-1685-1 perl security update
ELA-1676-2 postgresql-11 regression update
ELA-1677-2 postgresql-9.6 regression update
ELA-1686-1 mapserver security update
[DSA 6218-1] mupdf security update
[DLA 4538-1] perl security update

ELA-1685-1 perl security update

Package : perl

Version : 5.24.1-3+deb9u9 (stretch), 5.28.1-6+deb10u3 (buster)

Related CVEs :
CVE-2025-40909

Vincent Lefèvre discovered that, in the Perl programming language, at
thread creation the current directory may temporarily change in other
threads, altering file accesses. Under some conditions, a local
attacker may leverage this to access unauthorized data or even inject
arbitrary code.

ELA-1685-1 perl security update

ELA-1676-2 postgresql-11 regression update

Package : postgresql-11

Version : 11.22-0+deb10u8 (buster)

The fix for CVE-2026-2006 introduced a regression in SUBSTRING() for toasted
multibyte characters, as discussed in the upstream bug:
https://www.postgresql.org/message-id/19406-9867fddddd724fca@postgresql.org
Also a number of minor upstream fixes for the patches added in 11.22-0+deb10u7
where added:

pg_mblen_range, pg_mblen_with_len: Valgrind after encoding ereport.
Suppress new “may be used uninitialized” warning.
Fix test_valid_server_encoding helper function.
pgcrypto: Tweak error message for incorrect session key length.

ELA-1676-2 postgresql-11 regression update

ELA-1677-2 postgresql-9.6 regression update

Package : postgresql-9.6

Version : 9.6.24-0+deb9u12 (stretch)

The fix for CVE-2026-2006 introduced a regression in SUBSTRING() for toasted
multibyte characters, as discussed in the upstream bug:
https://www.postgresql.org/message-id/19406-9867fddddd724fca@postgresql.org
Also a number of minor upstream fixes for the patches added in 9.6.24-0+deb9u11
where added:

pg_mblen_range, pg_mblen_with_len: Valgrind after encoding ereport.
Suppress new “may be used uninitialized” warning.
Fix test_valid_server_encoding helper function.
pgcrypto: Tweak error message for incorrect session key length.

ELA-1677-2 postgresql-9.6 regression update

ELA-1686-1 mapserver security update

Package : mapserver

Version : 7.0.4-2+deb9u2 (stretch), 7.2.2-1+deb10u2 (buster)

Related CVEs :
CVE-2026-33721

A heap-buffer-overflow was found in mapserver, a CGI-based framework for
Internet map services, which could lead to Denial of Service via crafted
SLD (Styled Layer Descriptor) sent by a remote unauthenticated attacker.

ELA-1686-1 mapserver security update

[SECURITY] [DSA 6218-1] mupdf security update

- -------------------------------------------------------------------------
Debian Security Advisory DSA-6218-1 security@debian.org
https://www.debian.org/security/ Salvatore Bonaccorso
April 18, 2026 https://www.debian.org/security/faq
- -------------------------------------------------------------------------

Package : mupdf
CVE ID : CVE-2026-3308
Debian Bug : 1133189

A heap-based buffer overflow flaw was discovered in MuPDF, a lightweight
PDF viewer, which may result in denial of service or the execution of
arbitrary code if malformed documents are opened.

For the oldstable distribution (bookworm), this problem has been fixed
in version 1.21.1+ds2-1+deb12u1.

For the stable distribution (trixie), this problem has been fixed in
version 1.25.1+ds1-6+deb13u1.

We recommend that you upgrade your mupdf packages.

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

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

[SECURITY] [DLA 4538-1] perl security update

- -------------------------------------------------------------------------
Debian LTS Advisory DLA-4538-1 debian-lts@lists.debian.org
https://www.debian.org/lts/security/ Sylvain Beucler
April 18, 2026 https://wiki.debian.org/LTS
- -------------------------------------------------------------------------

Package : perl
Version : 5.32.1-4+deb11u5
CVE ID : CVE-2025-40909
Debian Bug : 1098226

Vincent Lefèvre discovered that, in the Perl programming language, at
thread creation the current directory may temporarily change in other
threads, altering file accesses. Under some conditions, a local
attacker may leverage this to access unauthorized data or even inject
arbitrary code.

For Debian 11 bullseye, this problem has been fixed in version
5.32.1-4+deb11u5.

We recommend that you upgrade your perl packages.

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

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