CVE-2018-16868
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 · uneditedA Bleichenbacher type side-channel based padding oracle attack was found in the way gnutls handles verification of RSA decrypted PKCS#1 v1.5 data. An attacker who is able to run process on the same physical core as the victim process, could use this to extract plaintext or in some cases downgrade any TLS connections to a vulnerable server.
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 · moderate confidenceA Bleichenbacher-type padding oracle vulnerability in GnuTLS allows an attacker with local code execution on the same physical CPU core as the victim process to extract plaintext from RSA-decrypted PKCS#1 v1.5 data by observing timing side-channels during padding verification, potentially enabling TLS connection downgrades.
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<= 3.6.4CVSS 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
- Physical
- Complexity
- High
- Privileges
- Low
- User interaction
- None
- Scope
- Changed
- Confidentiality
- High
- Integrity
- Low
- Availability
- None
CVSS:3.1/AV:P/AC:H/PR:L/UI:N/S:C/C:H/I:L/A:N
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 GnuTLS versionRun 'gnutls-cli --version' or 'gnutls-serv --version' from the command line, or query your package manager (e.g., 'dpkg -l | grep gnutls' on Debian/Ubuntu, 'rpm -qa | grep gnutls' on RHEL/CentOS)Affected if The version reported is 3.6.4 or lower
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Determine if RSA key exchange is in useReview your TLS server configuration files (e.g., /etc/gnutls/config, nginx/apache config if using GnuTLS) and check which cipher suites are enabled, specifically looking for 'RSA' or 'RSA-*' cipher suite definitionsAffected if RSA-based cipher suites (key exchange mechanisms using RSA decryption) are enabled in the TLS configuration
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Verify TLS connections use RSA key exchangeUse a TLS scanning tool such as 'gnutls-cli' or 'openssl s_client' to connect to your TLS services and inspect the negotiated cipher suite, or examine TLS handshake logs for the key exchange methodAffected if Connections are establishing with RSA key exchange (cipher suites like TLS_RSA_*); ECDHE and other forward-secret key exchanges are not affected by this specific oracle
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Assess local attack surfaceDetermine if untrusted local processes could share CPU cores with your GnuTLS processes by checking CPU affinity settings (e.g., 'taskset -pc <pid>' for running processes) or examining container/sandbox isolation configurationsAffected if GnuTLS processes handling RSA-decrypted TLS traffic share CPU cores with other local processes without proper isolation
You are affected if running GnuTLS version 3.6.4 or lower with RSA key exchange enabled and TLS connections using RSA key exchange are being handled by processes vulnerable to local timing observation.
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 GnuTLS to a patched version. Additionally, disable RSA key exchange and prefer ECDHE cipher suites to eliminate reliance on vulnerable RSA decryption, and consider physical isolation or CPU affinity controls to prevent co-location attacks.
- Consultation3.0 h
- Implementation4.0 h
- Testing8.0 h
- Review / QA3.0 h
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Free · runs locallyCheck whether your project pulls in CVE-2018-16868 — 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-2018-16868 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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- Version or environment caveats, and links to real fixes
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