dbcve.org
Enterprise Linux DesktopOperating system · Redhat

CVE-2016-8635

MEDIUM · 5.9 CVSS v3.0 Published 2018-08-01
Fix available
A fix is available. Upgrade to after 3.21.4 or later.
See remediation →
68/100
Remediation priority · Elevated
Remotely reachable No privileges Zero-click

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 · unedited
It was found that Diffie Hellman Client key exchange handling in NSS 3.21.x was vulnerable to small subgroup confinement attack. An attacker could use this flaw to recover private keys by confining the client DH key to small subgroup of the desired group.

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 confidence

NSS 3.21.x contains a flaw in Diffie-Hellman client key exchange handling where the implementation fails to validate that server-provided DH parameters generate a full-order group. This allows an attacker to confine the client's DH key to a small subgroup during the key exchange, enabling recovery of the private key through a small subgroup confinement attack.

MitigationUpgrade NSS to a version that properly validates DH parameters, specifically ensuring the server's DH group generates a full-order subgroup and rejecting parameters that would allow confinement to small subgroups.

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
Enterprise Linux DesktopOperating system
Affected:= 5.0= 6.0= 7.0
Enterprise Linux ServerOperating system
Affected:= 5.0= 6.0= 7.0
Enterprise Linux Server AusOperating system
Affected:= 7.3= 7.4= 7.6
Enterprise Linux Server EusOperating system
Affected:= 7.3= 7.4= 7.5= 7.6
Enterprise Linux Server TusOperating system
Affected:= 7.3= 7.6
Enterprise Linux WorkstationOperating system
Affected:= 5.0= 6.0= 7.0
Network Security ServicesApplication
Affected:>= 3.21, <= 3.21.4

CVSS 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
High
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None

CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/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 checks

Work through these to decide whether this CVE applies to you.

  1. Identify installed NSS package version
    Run 'rpm -qa | grep nss' on Red Hat systems, or check the NSS library version with 'rpm -q --qf '%{VERSION}' nss'
    Affected if Version is 3.21.x (specifically 3.21.0 through 3.21.4) or matches the listed RHEL 5.0, 6.0, or 7.0 variants
  2. Confirm RHEL variant and update level
    Run 'cat /etc/redhat-release' to identify the exact RHEL version (Desktop 5/6/7, Server 5/6/7, Workstation 5/6/7, or Server Aus/Eus/Tus variants)
    Affected if The system runs RHEL 5.0, 6.0, or 7.0, or any of the listed Server Aus/Eus/Tus variants (7.3, 7.4, 7.5, 7.6)
  3. Verify DH-based cipher suites are in use
    Check TLS server configuration for enabled cipher suites containing 'DHE' or 'EDH' (e.g., 'openssl ciphers -v' or review web server config files)
    Affected if The environment uses Diffie-Hellman (DHE/EDH) cipher suites in TLS connections, as this is the code path that triggers the vulnerable parameter validation
  4. Confirm NSS is the TLS provider
    Identify whether applications use NSS for TLS (common with Firefox, Thunderbird, and some server applications). Check with 'ldd <binary> | grep nss3' or review application TLS backend
    Affected if Applications or services rely on NSS for TLS/DH key exchanges, as only NSS implementations are affected by this specific flaw

A system is affected if it runs a vulnerable NSS version (3.21.x through 3.21.4) or a listed RHEL version (5.0, 6.0, 7.0 or related variants) AND utilizes Diffie-Hellman key exchange in TLS connections.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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 data
Upgrade available Upgrade to a release after 3.21.4
Interim mitigation

Upgrade NSS to a version that properly validates DH parameters, specifically ensuring the server's DH group generates a full-order subgroup and rejecting parameters that would allow confinement to small subgroups.

Fix this in Enterprise Linux Desktop Scoped from the published advisory
  • Consultation4.0 h
  • Implementation2.0 h
  • Testing6.0 h
  • Review / QA2.0 h
14.0 hours of engineering $2,420
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,872.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2016-8635 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

Get it on GitHub Scan in the browser

References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2016-8635 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • 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
  • No spam, self-promotion, credentials, or personal data