Description
Issue summary: The DTLS retransmission logic does not correctly handle
a handshake message write that is suspended part-way through.
The retransmitted message can be read past the message buffer and
the retransmission overwrites the internal state the suspended write
needs to resume correctly.

Impact summary: The retransmitted message can disclose a heap memory
to the peer as plaintext handshake data or cause a crash and a Denial
of Service when the read reaches an unmapped memory region.

CWE: CWE-125: Out-of-bounds Read

Description: DTLS handshake messages can be written out in multiple
fragments, and a write can suspend mid-message (returning WANT_WRITE)
if the underlying transport temporarily cannot accept more data. While
such a write is suspended, the DTLS retransmission timer may
independently fire and ask the retransmission logic to resend an
earlier, already-acknowledged-as-sent message from its retransmit
queue.

The retransmission logic reused the same internal buffer and position
tracking as the message that was still being written, without
resetting the position back to the start of the message being
retransmitted. As a result the retransmission was read starting from
wherever the suspended write had left off, producing a mislabelled
message whose body was leftover bytes from the other, larger message
still in flight - content that was never meant to be sent at that
point, and which could run past the end of the allocated buffer.

Separately, even when the retransmission is positioned correctly,
allowing it to run to completion while another write is suspended
overwrites the same shared bookkeeping that the suspended write
depends on to resume. When the application later resumes the
suspended write (via a subsequent SSL_read(), SSL_write(),
SSL_accept(), or SSL_connect() call), it finds that bookkeeping in a
state inconsistent with the message and aborts the process in
a debugging build.

The fix resets the retransmission's read position to the start of the
message before resending, and skips retransmission entirely whenever a
handshake write is still suspended, deferring to the next call that
resumes it instead.

FIPS impact: no
The affected code is outside the FIPS module boundary.
Published: 2026-09-29
Score: 8.2 High
EPSS: < 1% Very Low
KEV: No
Impact: Sensitive Data Exposure
Action: Apply Patch
AI Analysis

Impact

During a DTLS handshake, if a write operation is paused mid‑message, the retransmission timer may trigger and the retransmission logic incorrectly resumes from the suspended write’s buffer position. This causes the retransmitted packet to contain stray bytes that were not intended for that stage, making it possible for a remote peer to read data beyond the bounds of the intended message. The unintended read can leak internal heap memory to the attacker, exposing sensitive information. Additionally, the shared bookkeeping that the suspended write relies on is overwritten, which can lead to a crash and a denial of service when the application later attempts to resume the interrupted write.

Affected Systems

All OpenSSL deployments that use DTLS and have code prior to the security fix. Any release before the patches represented by the commits 906cf0ef1c85ca40ce69163e9086d6d3fe292943, 9f6b34422af7eb5dac61322e33dac1ae989fa628, a383dafdd754eb5b22bf45e37e1bff9d07277a58, or d951e02ede8f6a6ff8150546db44b34f0518192c is vulnerable.

Risk and Exploitability

The CVSS score of 8.2 indicates a high impact. EPSS is not available, and the vulnerability is not listed in CISA KEV. The most likely attack vector is an attacker who initiates or manipulates a DTLS handshake with the vulnerable OpenSSL instance to cause a suspended write and trigger the faulty retransmission logic. While the bug is publicly documented, there is currently no evidence of widespread exploitation in the wild, but the combination of data exposure and crash potential makes it a high priority risk.

Generated by OpenCVE AI on September 29, 2026 at 22:30 UTC.

Remediation

No solution or workaround provided in the CVE record.

OpenCVE Recommended Actions

  • Update OpenSSL to a fixed version that includes the fix from commit 906cf0ef1c85ca40ce69163e9086d6d3fe292943 or later.
  • If an immediate update is impossible, temporarily disable DTLS support on the affected servers so that retransmission logic is not exercised until the patch can be applied.
  • After applying the patch or making configuration changes, restart all services that use OpenSSL to ensure the new code is loaded.

Generated by OpenCVE AI on September 29, 2026 at 22:30 UTC.

Tracking

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Advisories
Source ID Title
Debian DLA Debian DLA DLA-4859-1 openssl security update
Debian DSA Debian DSA DSA-6531-1 openssl security update
Ubuntu USN Ubuntu USN USN-8847-1 OpenSSL vulnerabilities
History

Thu, 08 Oct 2026 01:30:00 +0000

Type Values Removed Values Added
CPEs cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:*

Wed, 30 Sep 2026 00:15:00 +0000

Type Values Removed Values Added
First Time appeared Redhat
Redhat hummingbird
CPEs cpe:/a:redhat:hummingbird:1
Vendors & Products Redhat
Redhat hummingbird
References
Metrics threat_severity

None

 threat_severity

Important

Tue, 29 Sep 2026 17:45:00 +0000

Type Values Removed Values Added
First Time appeared Openssl
Openssl openssl
Vendors & Products Openssl
Openssl openssl

Tue, 29 Sep 2026 17:30:00 +0000

Type Values Removed Values Added
Metrics cvssV3_1

{'score': 8.2, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H'}

ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Tue, 29 Sep 2026 15:45:00 +0000

Type Values Removed Values Added
Description Issue summary: The DTLS retransmission logic does not correctly handle a handshake message write that is suspended part-way through. The retransmitted message can be read past the message buffer and the retransmission overwrites the internal state the suspended write needs to resume correctly. Impact summary: The retransmitted message can disclose a heap memory to the peer as plaintext handshake data or cause a crash and a Denial of Service when the read reaches an unmapped memory region. CWE: CWE-125: Out-of-bounds Read Description: DTLS handshake messages can be written out in multiple fragments, and a write can suspend mid-message (returning WANT_WRITE) if the underlying transport temporarily cannot accept more data. While such a write is suspended, the DTLS retransmission timer may independently fire and ask the retransmission logic to resend an earlier, already-acknowledged-as-sent message from its retransmit queue. The retransmission logic reused the same internal buffer and position tracking as the message that was still being written, without resetting the position back to the start of the message being retransmitted. As a result the retransmission was read starting from wherever the suspended write had left off, producing a mislabelled message whose body was leftover bytes from the other, larger message still in flight - content that was never meant to be sent at that point, and which could run past the end of the allocated buffer. Separately, even when the retransmission is positioned correctly, allowing it to run to completion while another write is suspended overwrites the same shared bookkeeping that the suspended write depends on to resume. When the application later resumes the suspended write (via a subsequent SSL_read(), SSL_write(), SSL_accept(), or SSL_connect() call), it finds that bookkeeping in a state inconsistent with the message and aborts the process in a debugging build. The fix resets the retransmission's read position to the start of the message before resending, and skips retransmission entirely whenever a handshake write is still suspended, deferring to the next call that resumes it instead. FIPS impact: no The affected code is outside the FIPS module boundary.
Title DTLS Retransmits Handshake Messages From a Stale Buffer Offset
Weaknesses CWE-125
References

Subscriptions

Openssl Openssl
Redhat Hummingbird
cve-icon MITRE

Status: PUBLISHED

Assigner: openssl

Published:

Updated: 2026-09-29T16:45:40.378Z

Reserved: 2026-09-02T10:14:02.262Z

Link: CVE-2026-84782

cve-icon Vulnrichment

Updated: 2026-09-29T16:45:26.002Z

cve-icon NVD

Status : Analyzed

Published: 2026-09-29T16:17:12.500

Modified: 2026-10-08T01:20:56.003

Link: CVE-2026-84782

cve-icon Redhat

Severity : Important

Publid Date: 2026-09-29T00:00:00Z

Links: CVE-2026-84782 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-09-29T22:45:18Z

Weaknesses