# CVE-2026-84782: DTLS Retransmits Handshake Messages From a Stale Buffer Offset

> Attackers can trigger DTLS retransmission bugs to disclose heap memory or cause denial of service in applications using OpenSSL.

- **Severity:** High 8.2 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 29 Sep 2026
- **Updated:** 29 Sep 2026
- **Also known as:** ALPINE-CVE-2026-84782, ALSA-2026:76918, ALSA-2026:77396, ALSA-2026:80510, AZL-105363, AZL-105444, AZL-105483, AZL-105501, AZL-105567, AZL-105615, AZL-105696, AZL-105822, AZL-105864, BELL-CVE-2026-84782, CLEANSTART-2026-VF53508, CLSA-2026-1792066324, CLSA-2026-1792506549, CLSA-2026-1792537769, DEBIAN-CVE-2026-84782, ECHO-6278-6c73-07a6, GHSA-6w84-hw79-7wgf, MINI-r8m9-f3mg-2938, RHSA-2026:73496, RHSA-2026:76918, RHSA-2026:77396, RHSA-2026:80510, RLSA-2026:76918, RLSA-2026:77396, RLSA-2026:80510, ROOT-OS-ALPINE-315-CVE-2026-84782, ROOT-OS-ALPINE-317-CVE-2026-84782, SUSE-SU-2026:4418-1, SUSE-SU-2026:4560-1, UBUNTU-CVE-2026-84782

## What is CVE-2026-84782?

CVE-2026-84782 is a high-severity vulnerability in Openssl Openssl, published on 29 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-125 (Out-of-bounds Read)

## Which versions are affected by CVE-2026-84782?

It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `openssl` | AlmaLinux:10 | All versions | 1:3.5.8-2.el10_2.alma.1 |
| `openssl-devel` | AlmaLinux:10 | All versions | 1:3.5.8-2.el10_2.alma.1 |
| `openssl-libs` | AlmaLinux:10 | All versions | 1:3.5.8-2.el10_2.alma.1 |
| `openssl-perl` | AlmaLinux:10 | All versions | 1:3.5.8-2.el10_2.alma.1 |
| `compat-openssl10` | AlmaLinux:8 | All versions | 1:1.0.2o-4.el8_10.4 |
| `openssl` | AlmaLinux:9 | All versions | 1:3.5.8-2.el9_8 |
| `openssl-devel` | AlmaLinux:9 | All versions | 1:3.5.8-2.el9_8 |
| `openssl-libs` | AlmaLinux:9 | All versions | 1:3.5.8-2.el9_8 |
| `openssl-perl` | AlmaLinux:9 | All versions | 1:3.5.8-2.el9_8 |
| `openssl` | Red Hat:enterprise_linux:10.2 | All versions | 1:3.5.8-2.el10_2 |
| `openssl-debuginfo` | Red Hat:enterprise_linux:10.2 | All versions | 1:3.5.8-2.el10_2 |
| `openssl-debugsource` | Red Hat:enterprise_linux:10.2 | All versions | 1:3.5.8-2.el10_2 |
| `openssl-devel` | Red Hat:enterprise_linux:10.2 | All versions | 1:3.5.8-2.el10_2 |
| `openssl-libs` | Red Hat:enterprise_linux:10.2 | All versions | 1:3.5.8-2.el10_2 |
| `openssl-libs-debuginfo` | Red Hat:enterprise_linux:10.2 | All versions | 1:3.5.8-2.el10_2 |
| `openssl-perl` | Red Hat:enterprise_linux:10.2 | All versions | 1:3.5.8-2.el10_2 |
| `compat-openssl10` | Red Hat:enterprise_linux:8::appstream | All versions | 1:1.0.2o-4.el8_10.4 |
| `compat-openssl10-debuginfo` | Red Hat:enterprise_linux:8::appstream | All versions | 1:1.0.2o-4.el8_10.4 |
| `compat-openssl10-debugsource` | Red Hat:enterprise_linux:8::appstream | All versions | 1:1.0.2o-4.el8_10.4 |
| `openssl-debuginfo` | Red Hat:enterprise_linux:9::appstream | All versions | 1:3.5.8-2.el9_8 |
| `openssl-debugsource` | Red Hat:enterprise_linux:9::appstream | All versions | 1:3.5.8-2.el9_8 |
| `openssl-devel` | Red Hat:enterprise_linux:9::appstream | All versions | 1:3.5.8-2.el9_8 |
| `openssl-libs-debuginfo` | Red Hat:enterprise_linux:9::appstream | All versions | 1:3.5.8-2.el9_8 |
| `openssl-perl` | Red Hat:enterprise_linux:9::appstream | All versions | 1:3.5.8-2.el9_8 |
| `openssl` | Red Hat:enterprise_linux:9::baseos | All versions | 1:3.5.8-2.el9_8 |
| `openssl-debuginfo` | Red Hat:enterprise_linux:9::baseos | All versions | 1:3.5.8-2.el9_8 |
| `openssl-debugsource` | Red Hat:enterprise_linux:9::baseos | All versions | 1:3.5.8-2.el9_8 |
| `openssl-libs` | Red Hat:enterprise_linux:9::baseos | All versions | 1:3.5.8-2.el9_8 |
| `openssl-libs-debuginfo` | Red Hat:enterprise_linux:9::baseos | All versions | 1:3.5.8-2.el9_8 |
| `chunkah` | Red Hat:hummingbird:1 | All versions | 0:0.7.0-1.1.hum1 |
| `openssl` | Rocky Linux:10 | All versions | 1:3.5.8-2.el10_2 |
| `compat-openssl10` | Rocky Linux:8 | All versions | 1:1.0.2o-4.el8_10.4 |
| `openssl` | Rocky Linux:9 | All versions | 1:3.5.8-2.el9_8 |
| `openssl-3-livepatches` | SUSE:Linux Enterprise Live Patching 15 SP6 | All versions | 0.7-150600.13.22.1 |
| `openssl-3-livepatches` | SUSE:Linux Enterprise Live Patching 15 SP7 | All versions | 0.7-150700.16.15.1 |

Products: Openssl Openssl.

## How do I fix CVE-2026-84782?

Apply the vendor's patch.

## Is CVE-2026-84782 being exploited?

There is no known exploitation of CVE-2026-84782 in the wild and no public exploit code.

## Other vulnerabilities in Openssl Openssl

- [CVE-2009-3245](https://insights.sbomify.com/CVE-2009-3245/): Null dereference in n/a (critical 10.0)
- [CVE-2006-3738](https://insights.sbomify.com/CVE-2006-3738/): Memory corruption in n/a (critical 10.0)
- [CVE-2026-63073](https://insights.sbomify.com/CVE-2026-63073/): Untrusted Sender DN Used as Format String in CMP Response Validation (critical 9.8)
- [CVE-2016-6309](https://insights.sbomify.com/CVE-2016-6309/): Use after free in n/a (critical 9.8)
- [CVE-2016-0799](https://insights.sbomify.com/CVE-2016-0799/): Integer overflow in n/a (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-84782 and fix it if it is affected.

What it is: CVE-2026-84782 is a high-severity vulnerability in Openssl Openssl, published on 29 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-84782 in the wild and no public exploit code.

Affected product: Openssl Openssl. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-84782/ (Markdown: https://insights.sbomify.com/CVE-2026-84782/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-84782
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-84782
- OSV: https://osv.dev/vulnerability/CVE-2026-84782

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-84782/
Summaries are generated and may contain mistakes; the official description above is the record.