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No exploitation reportedFix availableAwaiting NVD analysis

CVE-2026-16318

No exploitation reported by the sources we read.

  • Published2026-07-21
  • WeaknessCWE-401

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

The QUIC transport parameters extension handler in s2n-tls incorrectly uses s2n_alloc instead of s2n_realloc to store the peer's transport parameters. When a TLS 1.3 connection goes through a HelloRetryRequest, the handler is called twice on the same connection. On the second call, s2n_alloc zeroes the existing pointer before allocating new memory, causing the first allocation to be leaked. This can occur during normal QUIC traffic when a client offers a key share group the server does not prefer. An unauthenticated user can amplify the issue by deliberately forcing HelloRetryRequests, causing up to approximately 64 KB of unreachable memory per handshake. Over time, this can lead to increased memory consumption on long-running server processes. The unreachable memory is only reclaimed when the process is restarted. Only server-side QUIC-enabled deployments are affected. Non-QUIC TLS connections are not affected. We recommend you upgrade s2n-tls to version v1.7.6

Timeline

dates in UTC
  1. 2026-07-2121:16CVE publishedNVD

Versions per branch

Products declared by the CNA1 product

As AMZN, the CNA that assigned this CVE, declared them in the CVE record; versions as written.

  • Amazon s2n-tlsother versions: not affected
    Affected
    • ≤ v1.7.5no fix statedcustom

Source: the CNA record (CVE Program), © The MITRE Corporation,CVE Terms of UseCVE recordupdated 2026-07-21

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

  • aws-efs-utilsSUSE:Linux Enterprise Module for Public Cloud 15 SP7all versions · fixed in 3.3.4-150600.17.12.1
  • aws-efs-utilsSUSE:Linux Enterprise Module for Public Cloud 15 SP6all versions · fixed in 3.3.4-150600.17.12.1
  • aws-efs-utilsopenSUSE:Tumbleweedall versions · fixed in 3.2.0-1.1
  • s2nopenSUSE:Tumbleweedall versions · fixed in 1.7.7-1.1
  • s2nopenSUSE:Leap 16.0all versions · fixed in 1.5.1-bp160.2.1

Vendor advisories

  • CVE-2026-16318 Red Hat Product Security

    s2n-tls: s2n-tls: Denial of Service due to memory leak in QUIC transport parameters handler

Full record on NVD

Fix

No fix published by the sources we read yet. NVD record

Detection

Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof of concept
Metasploit modules
none listed
Metasploit Framework

Sources

  • NVDCVE recordread 2026-10-25
  • CISA-ADPSSVC decisionnone2026-07-22
  • CNACVSS 4.06.9known since 2026-10-25
  • CNACVSS 3.15.3known since 2026-10-25
  • CNAweakness (CWE)CWE-401known since 2026-10-25
  • FIRST EPSSEPSS score0.4 %2026-11-08
  • OSVaffected packages—

Identifiers

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
CVSS 4.0 vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Published
2026-07-21
Last Modified
2026-10-24
NVD status
Awaiting Analysis

Frequently asked questions

What is CVE-2026-16318?

The QUIC transport parameters extension handler in s2n-tls incorrectly uses s2n_alloc instead of s2n_realloc to store the peer's transport parameters. When a TLS 1.3 connection goes through a HelloRetryRequest, the handler is called twice on the same connection. On the second call, s2n_alloc zeroes the existing pointer before allocating new memory, causing the first allocation to be leaked. This can occur during normal QUIC traffic when a client offers a key share group the server does not prefer. An unauthenticated user can amplify the issue by deliberately forcing HelloRetryRequests, causing up to approximately 64 KB of unreachable memory per handshake. Over time, this can lead to increased memory consumption on long-running server processes. The unreachable memory is only reclaimed when the process is restarted. Only server-side QUIC-enabled deployments are affected. Non-QUIC TLS connections are not affected. We recommend you upgrade s2n-tls to version v1.7.6

Is CVE-2026-16318 actively exploited?

Active exploitation of CVE-2026-16318 has not been confirmed. Its EPSS score was 0.4% on 2026-11-08, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2026-16318?

CVE-2026-16318 has a CVSS v3 base score of 5.3 (MEDIUM severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L.

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