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CVE-2026-16318

QUIC Transport Parameters Memory Leak During HelloRetryRequest in s2n-tls

6.9 Medium

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

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
None
Integrity
None
Availability
Low

Exploit likelihood

0.39%Unchanged since Jul 22, 2026
90%50%10%1%

What each source reports

CVE List Score used 6.9

QUIC Transport Parameters Memory Leak During HelloRetryRequest in s2n-tls

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

Record
CVE-2026-16318
CVSS 4.0
6.9 MediumCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
CVSS 3.1
5.3 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Weakness
CWE-401
Updated
2026-11-02
EUVDEUVD-2026-46402 6.9

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

Record
EUVD-2026-46402
CVSS 4.0
6.9 MediumCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
Updated
2026-11-02
NVD 6.9

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

Record
CVE-2026-16318
CVSS 4.0
6.9 MediumCVSS: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
CVSS 3.1
5.3 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Weakness
CWE-401
Updated
2026-11-02
OSV 6.9

QUIC Transport Parameters Memory Leak During HelloRetryRequest in s2n-tls

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

Record
CVE-2026-16318
CVSS 4.0
6.9 MediumCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
Weakness
CWE-401
Updated
2026-11-05
OSVopenSUSE-SU-2026:11492-1 No score

aws-efs-utils-3.2.0-1.1 on GA media

These are all security issues fixed in the aws-efs-utils-3.2.0-1.1 package on the GA media of openSUSE Tumbleweed.

Record
openSUSE-SU-2026:11492-1
Updated
2026-11-02
OSVopenSUSE-SU-2026:11526-1 No score

libs2n1-1.7.7-1.1 on GA media

These are all security issues fixed in the libs2n1-1.7.7-1.1 package on the GA media of openSUSE Tumbleweed.

Record
openSUSE-SU-2026:11526-1
Updated
2026-11-02
OSVopenSUSE-SU-2026:21474-1 No score

Security update for s2n

This update for s2n fixes the following issues:

Changes in s2n:

  • CVE-2026-16318: Denial of Service due to memory leak in QUIC transport parameters handler (bsc#1272352)
  • CVE-2026-16317: man-in-the-middle attack can silently discard individual application data records
Record
openSUSE-SU-2026:21474-1
Updated
2026-11-02
OSVopenSUSE-SU-2026:21501-1 No score

Security update for s2n

This update for s2n fixes the following issues:

Changes in s2n:

  • CVE-2026-16318: Denial of Service due to memory leak in QUIC transport parameters handler (bsc#1272352)
  • CVE-2026-16317: man-in-the-middle attack can silently discard individual application data records
Record
openSUSE-SU-2026:21501-1
Updated
2026-11-02
OSVSUSE-SU-2026:5101-1 No score

Security update for aws-efs-utils

This update for aws-efs-utils fixes the following issues:

Security issues fixed:

  • CVE-2026-16317: s2n-tls: man-in-the-middle attack can silently discard individual application data records (bsc#1272354).
  • CVE-2026-16318: s2n-tls: Denial of Service due to memory leak in QUIC transport parameters handler (bsc#1272349).
  • CVE-2026-25541: bytes: integer overflow in 'BytesMut:reserve' can lead to undefined behavior and crashes (bsc#1274202).

Changes for aws-efs-utils:

  • Update to version 3.3.4
Record
SUSE-SU-2026:5101-1
Updated
2026-11-05

Affected products

Affected packages

Affected packages
PackageAffectedFixed
aws-efs-utils
SUSE:Linux Enterprise Module for Public Cloud 15 SP6
From an advisory covering 3 CVEs
 before 3.3.4-150600.17.12.1
3.3.4-150600.17.12.1
aws-efs-utils
SUSE:Linux Enterprise Module for Public Cloud 15 SP7
From an advisory covering 3 CVEs
 before 3.3.4-150600.17.12.1
3.3.4-150600.17.12.1
aws-efs-utils
openSUSE:Tumbleweed
From an advisory covering 3 CVEs
 before 3.2.0-1.1
3.2.0-1.1
s2n
openSUSE:Tumbleweed
From an advisory covering 2 CVEs
 before 1.7.7-1.1
1.7.7-1.1
s2n
openSUSE:Leap 16.0
From an advisory covering 2 CVEs
 before 1.5.1-bp160.2.1
1.5.1-bp160.2.1

History

History
RecordedChangedSources
affected, facts
affected, aliases, facts, referencesOSV
affected
first indexedCVE List, EUVD, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-16318 is a medium vulnerability (CVSS 6.9) in Amazon S2n-tls, published July 21, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.39%, the 33rd percentile. No source names a fixed version.

References

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