CVE-2026-16318

MEDIUMPre-NVD 5.35.3
EchelonGraph scoreLOW confidence

This medium-severity CVE scores 5.3 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit-prediction score not yet available (the EPSS model rescores nightly; freshly-published CVEs typically appear within 48 hours). GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: secondary
Trending — 3 sources updated this week
5.3
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS: 0%CVSS: 5.3Exploit: NoneExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

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

CVSS v3
5.3
EG Score
5.3(low)
EPSS
31.3%
KEV
Not listed

Published

July 21, 2026

Last Modified

July 21, 2026

Advisory Details (2)

Auto-updated Jul 21, 2026
Patch available. Sources: github_release, github.
github Patch Available

QUIC Transport Parameters Memory Leak During HelloRetryRequest in s2n-tls · Advisory · aws/s2n-tls · GitHub

https://github.com/aws/s2n-tls/security/advisories/GHSA-cr7x-863j-xrc7
github_release Patch Available

v1.7.6

Patch available: aws/s2n-tls v1.7.6

https://github.com/aws/s2n-tls/releases/tag/v1.7.6

Vendor Advisories for CVE-2026-16318(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 4× in last 7d / 4× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-07-22 14:08 UTCEPSS rescore
  2. 2026-07-21 21:24 UTCEG score recompute
  3. 2026-07-21 20:45 UTCEG score recompute
  4. 2026-07-21 20:43 UTCMITRE cvelistV5first tracked

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2026-16318?
CVE-2026-16318 is a medium vulnerability published on July 21, 2026. The QUIC transport parameters extension handler in s2n-tls incorrectly uses s2nalloc instead of s2nrealloc 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…
When was CVE-2026-16318 disclosed?
CVE-2026-16318 was first published in the National Vulnerability Database on July 21, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-16318 actively exploited?
CVE-2026-16318 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 31.3% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2026-16318?
CVE-2026-16318 has a CVSS v3 base score of 5.3 (NVD). The EG score is currently aggregating — additional source signals are being incorporated as they become available..
How do I remediate CVE-2026-16318?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-16318, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

Explore the affected products and dependency analysis for CVE-2026-16318

Explore →

Is Your Infrastructure Affected by CVE-2026-16318?

EchelonGraph automatically scans your cloud infrastructure and maps CVE exposure using blast radius analysis.

Start Free Scan →Browse All CVEs