On 29 September 2026 the OpenSSL project published a security advisory covering fourteen issues. Debian released DSA-6531-1 for Debian 13 (trixie) on 30 September, fixing 13 of them, and the Debian LTS team followed with DLA-4859-1 for Debian 12 (bookworm) on 26 October for the six issues that affect OpenSSL 3.0. OpenSSL rates one issue High and the rest Low.
At a glance
| Item | Details |
|---|---|
| Source package | openssl |
| Debian 13 (trixie) | Fixed in 3.5.7-1~deb13u3 (DSA-6531-1, 30 Sep 2026) |
| Debian 12 (bookworm) | Fixed in 3.0.22-1~deb12u2 (DLA-4859-1, 26 Oct 2026) |
| Binary packages to check | openssl, libssl3t64 (trixie) or libssl3 (bookworm), plus libssl-dev if installed |
| CVEs | 13 in DSA-6531-1; 6 of them in DLA-4859-1 |
| Severity | High for CVE-2026-84782 (OpenSSL rating); all others Low |
| Upstream advisory | OpenSSL secadv 20260929 |
What the vulnerabilities are
Debian summarises the set as issues that "could result in denial of service, information disclosure or potentially recovery of private keys". In plain terms:
- DTLS retransmission bug (CVE-2026-84782, High). When a DTLS handshake write is paused and the retransmit timer fires, OpenSSL could resend data from the wrong buffer position. OpenSSL says this can disclose heap memory to the peer or crash the process. It affects every supported branch, including the 3.0 and 3.5 lines Debian ships, but only software that uses DTLS (the UDP variant of TLS).
- DTLS 1.2 teardown (CVE-2026-75806, Low). A single unauthenticated, undersized datagram can end an existing DTLS 1.2 session that uses an AEAD cipher. No memory-safety or confidentiality impact.
- Timing side channels (CVE-2026-54872, CVE-2026-77696, CVE-2026-54875, Low). ECDSA signing on generic curves such as Brainpool, and SM2 signing, could leak timing information about the secret nonce. OpenSSL notes the leak is very small and that the NIST curves P-256, P-384 and P-521 use dedicated constant-time code. This is the "recovery of private keys" risk in Debian's text, and it needs many precise measurements.
- Certificate memory pressure (CVE-2026-35189, Low). A crafted certificate with many relative CRL distribution points can cause heavy memory use in clients, or in servers that request client certificates.
- CMP client crash (CVE-2026-75805, Low). A crafted revocation response can crash a Certificate Management Protocol client.
- QUIC issues (CVE-2026-35191, CVE-2026-42772, CVE-2026-54873, CVE-2026-75804, CVE-2026-84784, Low). Amplification, CPU and memory exhaustion in OpenSSL's own QUIC stack. They affect only OpenSSL 3.4 or 3.5 and later, so Debian 13 only.
- SSL_set_SSL_CTX() out-of-bounds access (CVE-2026-72897, Low). Only TLS servers that switch context mid-handshake in an unusual, non-default provider setup. OpenSSL 3.4 and later only.
The fourteenth issue in the upstream advisory, CVE-2026-84783 (Moderate), affects only OpenSSL 4.0, which neither Debian 12 nor Debian 13 ships. None of these CVEs is listed in the CISA Known Exploited Vulnerabilities catalog as of 30 October 2026.
Debian 12 also received DLA-4795-1 on 25 September (version 3.0.22-1~deb12u1) for six earlier OpenSSL issues. If you stopped there, you still need the newer ~deb12u2 build.
Are you affected?
Almost every Debian server has libssl installed, if only because openssh-server depends on it, so the question is which version you run:
dpkg-query -W -f='${Package} ${Version}\n' openssl 'libssl3*'
apt policy libssl3t64 # Debian 13
apt policy libssl3 # Debian 12Compare the Installed line with 3.5.7-1~deb13u3 (trixie) or 3.0.22-1~deb12u2 (bookworm). Anything older needs the update. Debian 11 (bullseye) left LTS on 31 August 2026 and receives no further Debian fixes; plan an upgrade.
How to update
sudo apt update
sudo apt upgradeTo update only OpenSSL:
sudo apt install --only-upgrade openssl libssl3t64 # Debian 13
sudo apt install --only-upgrade openssl libssl3 # Debian 12Ubuntu ships different OpenSSL builds; check Ubuntu Security Notices instead of using the Debian versions above.
Restart or reboot?
No reboot is required for the library itself, but every running program that loaded the old libssl keeps using it until it restarts. Typical examples are web servers, mail servers, VPN daemons and language runtimes. The needrestart package lists them:
sudo apt install needrestart
sudo needrestart -r lRestart what it reports, for example sudo systemctl restart nginx. On a small server a planned reboot is the simplest way to be sure nothing still holds the old library.
Sources
- security-tracker.debian.org/tracker/DSA-6531-1
- debian.org/security/2026/dsa-6531
- lists.debian.org/debian-security-announce/2026/msg00444.html
- security-tracker.debian.org/tracker/DLA-4859-1
- lists.debian.org/debian-lts-announce/2026/10/msg00053.html
- security-tracker.debian.org/tracker/DLA-4795-1
- lists.debian.org/debian-lts-announce/2026/09/msg00030.html
- openssl-library.org/news/secadv/20260929.txt
- cve.org/CVERecord?id=CVE-2026-84782
- cve.org/CVERecord?id=CVE-2026-84783
- security-tracker.debian.org/tracker/openssl
- packages.debian.org/source/trixie/openssl
- packages.debian.org/source/bookworm/openssl
- manpages.debian.org/trixie/needrestart/needrestart.1.en.html
- debian.org/releases
- packages.debian.org/trixie/openssh-server
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