CVE-2022-40735
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 Diffie-Hellman Key Agreement Protocol allows use of long exponents that arguably make certain calculations unnecessarily expensive, because the 1996 van Oorschot and Wiener paper found that "(appropriately) short exponents" can be used when there are adequate subgroup constraints, and these short exponents can lead to less expensive calculations than for long exponents. This issue is different from CVE-2002-20001 because it is based on an observation about exponent size, rather than an observation about numbers that are not public keys. The specific situations in which calculation expense would constitute a server-side vulnerability depend on the protocol (e.g., TLS, SSH, or IKE) and the DHE implementation details. In general, there might be an availability concern because of server-side resource consumption from DHE modular-exponentiation calculations. Finally, it is possible for an attacker to exploit this vulnerability and CVE-2002-20001 together.
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 confidenceThe Diffie-Hellman Key Agreement Protocol (DHE) allows clients to propose excessively long exponents during key exchange, causing unnecessary computational overhead due to expensive modular-exponentiation calculations on the server side. This creates a denial-of-service vulnerability where an attacker can exhaust server resources by sending multiple key exchange requests with large exponents.
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 dataall versionsCVSS 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:3.1/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 services using DHE key exchangeReview TLS server configurations (e.g., openssl.cnf, nginx.conf, httpd.conf) and look for DHE or EDH cipher suites (such as DHE-RSA-AES256-SHA, DHE-RSA-CHACHA20-POLY1305). Check SSH configuration files (sshd_config) for diffie-hellman-group-exchange-sha* key exchange methods. Check IKE/IPSec configurations for DH group settings.Affected if DHE cipher suites are enabled in TLS, SSH uses diffie-hellman-group-exchange methods, or IKE is configured with DH groups without exponent size constraints
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Check for maximum exponent size limitsInspect TLS libraries (OpenSSL, GnuTLS), SSH daemon settings, and IPsec/IKE daemon configurations for any directives that limit the maximum DH exponent bit length (such as 'dh_max_bits', 'MaxDHBits', or similar settings). Review application-level TLS settings for explicit exponent length restrictions.Affected if No maximum exponent size limit is configured or the limit is set excessively high (e.g., above 8192 bits for common servers)
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Check for rate limiting or resource controls on key exchangeReview firewall rules, load balancer configurations, and application-level rate limiting that may restrict the number of key exchange requests per client or per time window. Check if services implement connection limits or request throttling for new TLS handshakes using DHE.Affected if No rate limiting or resource controls exist on DHE key exchange operations, allowing unlimited requests from a single source
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Monitor for excessive DH key exchange computational patternsReview server performance metrics and logs for unusually high CPU usage correlated with TLS handshake activity. Use tools like 'openssl speed dh' to benchmark DH operations and compare against baseline. Monitor for repeated slow key exchanges or connection timeouts during DHE negotiation.Affected if Servers show high CPU usage during TLS handshakes with DHE cipher suites, or logs indicate slow key exchange completion times
A system is affected if DHE key exchange is enabled in any TLS, SSH, or IKE configuration without limits on accepted exponent sizes or without rate limiting on key exchange requests.
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.
dbcve · scopedDisable or restrict DHE cipher suites in TLS, SSH, and IKE configurations, or implement constraints on maximum exponent sizes accepted by the server to prevent computationally expensive key exchanges.
- Review TLS, SSH, and IKE server configurations to identify DHE (Diffie-Hellman key exchange) usage
- For TLS servers: Configure the server to either disable DHE or limit the maximum DHE group size (e.g., restrict to 2048-bit groups or smaller)
- For SSH servers: Configure the server to limit DH key sizes in the configuration (e.g., using the KexAlgorithms option with restricted key sizes)
- For IKE/IPSec: Configure the VPN gateway to restrict DH group usage to recommended groups (e.g., RFC 7919 groups or well-known safe primes)
- Implement rate limiting or connection limits on servers handling DHE key exchanges to mitigate resource exhaustion
- Monitor server resource usage and logs for signs of DHE-based DoS attempts
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation4.0 h
- Implementation6.0 h
- Testing2.0 h
- Review / QA2.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2022-40735 — 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-2022-40735 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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