dbcve.org
H2oApplication · Dena

CVE-2023-50247

HIGH · 7.5 CVSS v3.1 Published 2023-12-12
Fix available
A fix is available. Upgrade to after 2.2.6 or later.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges Zero-click Patch available

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
h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. The QUIC stack (quicly), as used by H2O up to commit 43f86e5 (in version 2.3.0-beta and prior), is susceptible to a state exhaustion attack. When H2O is serving HTTP/3, a remote attacker can exploit this vulnerability to progressively increase the memory retained by the QUIC stack. This can eventually cause H2O to abort due to memory exhaustion. The vulnerability has been resolved in commit d67e81d03be12a9d53dc8271af6530f40164cd35. HTTP/1 and HTTP/2 are not affected by this vulnerability as they do not use QUIC. Administrators looking to mitigate this issue without upgrading can disable HTTP/3 support.

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
How this class of weakness works · CWE-770

The application allocates memory, connections, or handles in response to a request without enforcing any cap, so a modest amount of malicious traffic exhausts the resource and denies service to everyone else. The fix is enforcing quotas, limits, and timeouts on what any single request or client can consume.

General guidance for the resource allocation without limits class — the official description and references above are authoritative for this specific CVE. Want a bespoke review and a reviewed fix? Ask our team →

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
H2oApplication
Affected:<= 2.2.6= 2.3.0

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
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

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 · scoped
Upgrade available Upgrade to a release after 2.2.6
Vendor patch github.com →
Recommended fix Moderate confidence

H2O version 2.4.0 or later (any release containing commit d67e81d03be12a9d53dc8271af6530f40164cd35)

  1. 1. Identify the current H2O version by running `h2o --version`
  2. 2. Download or upgrade to a release version that includes the fix commit d67e81d (version 2.4.0 or later)
  3. 3. If using a package manager, update the package (e.g., `apt update && apt upgrade h2o` or `brew upgrade h2o`)
  4. 4. Alternatively, rebuild from source using a version after commit d67e81d03be12a9d53dc8271af6530f40164cd35
  5. 5. Verify the upgrade was successful by running `h2o --version`
  6. 6. Test HTTP/3 functionality if applicable
  7. 7. As an alternative mitigation (if upgrade is not immediately possible), disable HTTP/3 by removing or commenting out the `listen:` directive with `alpn: [h3]` in the configuration file
Caveat Ensure any existing HTTP/3 client configurations are compatible; minor version upgrades in H2O typically maintain configuration compatibility

Generated from the published advisory — verify against the referenced sources before acting.

We can identify the exact fixed release, upgrade, and verify it in staging — typical engagement from $1,950. Get the upgrade done

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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-2023-50247 in production — separate from our analysis above.

No notes yet

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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
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