FreeBSD 15 — py35-cryptography — multiple vulnerabilities (2 CVEs) — patch and remediation guide

📖 ~4 min read  •  Source: FreeBSD VuXML

VuXML topic: py-cryptography — tag forgery vulnerability

Related CVEs: CVE-2016-9243 CVE-2018-10903

Upstream summary: The Python Cryptographic Authority (PyCA) project reports: finalize_with_tag() allowed tag truncation by default which can allow tag forgery in some cases. The method now enforces the min_tag_length provided to the GCM constructor

Table of contents

1. Symptom & Impact
2. Environment & Reproduction
3. Root Cause Analysis
4. Quick Triage
5. Step-by-Step Diagnosis
6. Solution – Primary Fix
7. Solution – Alternative Approaches
8. Verification & Acceptance Criteria
9. Rollback Plan
10. Prevention & Hardening
11. Related Errors & Cross-Refs
12. References & Further Reading

Symptom & Impact

On FreeBSD 15 hosts running py35-cryptography, operators see behaviour consistent with the FreeBSD VuXML entry: pkg audit flags the installed version, services may refuse to start after upgrade or restart, and — for security-rated advisories — the host is exposed to the vulnerabilities above. Impact spans isolated service restart cycles to full availability incidents on jails or bhyve guests that depend on py35-cryptography.

Environment & Reproduction

Reproduction targets FreeBSD 15. Confirm with freebsd-version -kru, uname -a, and the installed package via pkg info py35-cryptography and pkg query "%n-%v" py35-cryptography. Capture system state with pkg audit -F and service -e. Trigger the workflow that exposes py35-cryptography — multiple vulnerabilities (2 CVEs) — patch and remediation guide while collecting tail -200 /var/log/messages, dmesg -a, and /var/log/pkg.log.

Root Cause Analysis

Root cause is tracked at FreeBSD VuXML. The FreeBSD ports security team shipped a corrective py35-cryptography port revision; hosts on an outdated build remain exposed. Correlate /var/log/pkg.log with /var/log/messages and kernel state in sysctl kern.lastpid + sysctl kern.osreldate to isolate the change that triggered the failure mode.

Quick Triage

Quick triage: service py35-cryptography status, tail -100 /var/log/messages, pkg audit -F, pkg version -v py35-cryptography, and pfctl -sr (or ipfw list) to confirm firewall posture. For kernel issues: dmesg -a | tail -100 and kldstat.

Step-by-Step Diagnosis

1) service -e to enumerate failed services. 2) tail -F /var/log/messages and dmesg. 3) Validate firewall via pfctl -sr -v or ipfw show. 4) pkg check -B py35-cryptography for integrity. 5) pkg install -fy py35-cryptography to reinstall if tampered. 6) Correlate findings with /var/log/pkg.log and FreeBSD VuXML to pin the commit that introduced py35-cryptography — multiple vulnerabilities (2 CVEs) — patch and remediation guide.

Solution – Primary Fix

Primary fix: install the corrective py35-cryptography port revision referenced by FreeBSD VuXML. Typical commands: sudo pkg update, sudo pkg upgrade py35-cryptography (or sudo pkg upgrade -y for the whole system), then sudo service py35-cryptography restart, and pkg audit to confirm no remaining advisories. For ports tree builders: sudo portsnap fetch update + cd /usr/ports/<cat>/py35-cryptography && sudo make deinstall reinstall clean. Reboot if the kernel module is involved.

Solution – Alternative Approaches

Alternatives include locking the package with sudo pkg lock py35-cryptography until vetted, downgrading via pkg install <older-version> from a pinned repo, switching the FreeBSD pkg repository between quarterly and latest in /usr/local/etc/pkg/repos/FreeBSD.conf, isolating the affected service in a jail (iocage/bastille) with stricter firewall rules, or replacing the service with a vendored static build for the period between exposure detection and full rollout.

Verification & Acceptance Criteria

Acceptance: pkg info py35-cryptography shows the expected fixed version, service py35-cryptography status is running, pkg audit returns no advisory for py35-cryptography, tail -50 /var/log/messages shows no errors after restart, and the original reproduction for py35-cryptography — multiple vulnerabilities (2 CVEs) — patch and remediation guide no longer triggers across two consecutive runs.

Rollback Plan

Capture state with pkg query "%n-%v" > /root/pkg-pre.txt and a ZFS boot-environment snapshot: bectl create pre-py35-cryptography-patch. To revert, run sudo pkg install -f <previous-version> or boot the previous BE via bectl activate pre-py35-cryptography-patch && reboot. For kernel/loader changes, drop to the loader prompt and select the previous boot environment.

Prevention & Hardening

Prevent recurrence by scheduling pkg audit -F via periodic.conf (daily_status_security_pkgaudit_enable="YES"), subscribing to freebsd-security-notifications, mirroring through a local pkg repo managed by poudriere, version-pinning sensitive packages with pkg lock, enabling automatic ZFS BE snapshots before upgrades, and monitoring file integrity via mtree or aide. Apply the CIS FreeBSD hardening checklist where applicable and harden jails with allow.* tunables in /etc/jail.conf.

Related Errors & Cross-Refs

Related issues that commonly surface alongside py35-cryptography — multiple vulnerabilities (2 CVEs) — patch and remediation guide: pkg lock contention, mismatched ABI after kernel/userland skew (freebsd-version vs uname -K), pf rule drift, and stale shared-library references after upgrade (pkg check -d).

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References & Further Reading

Primary reference: FreeBSD VuXML. Supporting docs: FreeBSD Handbook, man pkg, man freebsd-update, man pfctl, man ipfw, man bectl, man periodic.conf, the FreeBSD Security Advisories at security.freebsd.org, and /usr/ports/UPDATING for port-specific notes implicated in py35-cryptography — multiple vulnerabilities (2 CVEs) — patch and remediation guide.