Ubuntu LinuxOperating system · Canonical
CVE-2016-4356
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedThe append_utf8_value function in the DN decoder (dn.c) in Libksba before 1.3.3 allows remote attackers to cause a denial of service (out-of-bounds read) by clearing the high bit of the byte after invalid utf-8 encoded data.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceLibksba before 1.3.3 contains an out-of-bounds read vulnerability in the DN decoder's append_utf8_value function in dn.c. The vulnerability is triggered when processing invalid UTF-8 encoded data followed by a byte where the high bit is cleared, causing the decoder to read beyond buffer boundaries and leading to denial of service.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data
Ubuntu LinuxOperating system
= 12.04= 14.04<= 1.3.2CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify installed libksba version on UbuntuRun 'dpkg -l | grep libksba' or 'apt show libksba' to list the installed package versionAffected if The version listed is 1.3.2 or earlier, or no version is shown because the package is not installed but older binaries exist
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Check Ubuntu release versionRun 'lsb_release -r' or check /etc/lsb-release to determine the Ubuntu versionAffected if The system runs Ubuntu 12.04 or Ubuntu 14.04 and has libksba installed
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Locate libksba library file and versionRun 'find /usr -name "*ksba*" -type f' to find library files, then use 'strings' or check the file metadata for version infoAffected if A libksba shared library file exists and reports version 1.3.2 or earlier when inspected
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Identify applications using libksbaRun 'ldconfig -p | grep ksba' to list programs that link against libksba, or use 'ldd' on binaries like gpg, gpgsm, or kleopatraAffected if Any application is dynamically linked to a vulnerable libksba version (1.3.2 or earlier)
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Verify DN decoder usage contextCheck if the system processes X.509 certificates, S/MIME messages, or handles certificate requests using affected binariesAffected if The system processes user-supplied or untrusted certificate/DN data through tools that rely on libksba's dn.c decoder functions
A user is affected if their system has libksba version 1.3.2 or earlier installed, particularly on Ubuntu 12.04 or 14.04, and uses applications that process X.509 or S/MIME data through the DN decoder.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor dataUpdate Libksba to version 1.3.3 or later to obtain the patched code. Recompile and redeploy any applications that statically link against the vulnerable library version.
Fix this in Ubuntu Linux
Scoped from the published advisory
- Consultation2.0 h
- Implementation4.0 h
- Testing3.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,088.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2016-4356 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2016-4356 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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