CVE-2026-84782 (GCVE-0-2026-84782)
Vulnerability from cvelistv5 – Published: 2026-09-29 15:32 – Updated: 2026-11-10 12:49
VLAI
EPSS
VEX
Title
DTLS Retransmits Handshake Messages From a Stale Buffer Offset
Summary
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.
Severity
8.2 (High)
SSVC
Exploitation: none
Automatable: yes
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-09-29 16:45 UTC
CWE
- CWE-125 - Out-of-bounds Read
Assigner
References
6 references
Impacted products
6 products
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| OpenSSL | OpenSSL |
Affected:
4.0.0 , < 4.0.3
(semver)
Affected: 3.6.0 , < 3.6.5 (semver) Affected: 3.5.0 , < 3.5.9 (semver) Affected: 3.4.0 , < 3.4.8 (semver) Affected: 3.0.0 , < 3.0.23 (semver) Affected: 1.1.1 , < 1.1.1zj (custom) Affected: 1.0.2 , < 1.0.2zs (custom) |
guessed | |
| Siemens | SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0) |
Affected:
V3.1.7 , < *
(custom)
|
guessed | |
| Siemens | SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0) |
Affected:
V3.1.7 , < *
(custom)
|
guessed | |
| Siemens | SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0) |
Affected:
V3.1.7 , < *
(custom)
|
guessed | |
| Siemens | SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0) |
Affected:
V3.1.7 , < *
(custom)
|
guessed | |
| Siemens | SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0) |
Affected:
V3.1.7 , < *
(custom)
|
guessed |
Date Public
2026-09-29 14:21
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"value": "Issue summary: The DTLS retransmission logic does not correctly handle\u003cbr\u003ea handshake message write that is suspended part-way through.\u003cbr\u003eThe retransmitted message can be read past the message buffer and\u003cbr\u003ethe retransmission overwrites the internal state the suspended write\u003cbr\u003eneeds to resume correctly.\u003cbr\u003e\u003cbr\u003eImpact summary: The retransmitted message can disclose a heap memory\u003cbr\u003eto the peer as plaintext handshake data or cause a crash and a Denial\u003cbr\u003eof Service when the read reaches an unmapped memory region.\u003cbr\u003e\u003cbr\u003eCWE: CWE-125: Out-of-bounds Read\u003cbr\u003e\u003cbr\u003eDescription: DTLS handshake messages can be written out in multiple\u003cbr\u003efragments, and a write can suspend mid-message (returning WANT_WRITE)\u003cbr\u003eif the underlying transport temporarily cannot accept more data. While\u003cbr\u003esuch a write is suspended, the DTLS retransmission timer may\u003cbr\u003eindependently fire and ask the retransmission logic to resend an\u003cbr\u003eearlier, already-acknowledged-as-sent message from its retransmit\u003cbr\u003equeue.\u003cbr\u003e\u003cbr\u003eThe retransmission logic reused the same internal buffer and position\u003cbr\u003etracking as the message that was still being written, without\u003cbr\u003eresetting the position back to the start of the message being\u003cbr\u003eretransmitted. As a result the retransmission was read starting from\u003cbr\u003ewherever the suspended write had left off, producing a mislabelled\u003cbr\u003emessage whose body was leftover bytes from the other, larger message\u003cbr\u003estill in flight - content that was never meant to be sent at that\u003cbr\u003epoint, and which could run past the end of the allocated buffer.\u003cbr\u003e\u003cbr\u003eSeparately, even when the retransmission is positioned correctly,\u003cbr\u003eallowing it to run to completion while another write is suspended\u003cbr\u003eoverwrites the same shared bookkeeping that the suspended write\u003cbr\u003edepends on to resume. When the application later resumes the\u003cbr\u003esuspended write (via a subsequent SSL_read(), SSL_write(),\u003cbr\u003eSSL_accept(), or SSL_connect() call), it finds that bookkeeping in a\u003cbr\u003estate inconsistent with the message and aborts the process in\u003cbr\u003ea debugging build.\u003cbr\u003e\u003cbr\u003eThe fix resets the retransmission\u0027s read position to the start of the\u003cbr\u003emessage before resending, and skips retransmission entirely whenever a\u003cbr\u003ehandshake write is still suspended, deferring to the next call that\u003cbr\u003eresumes it instead.\u003cbr\u003e\u003cbr\u003eFIPS impact: no\u003cbr\u003eThe affected code is outside the FIPS module boundary."
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}
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Drag nodes to arrange them. Double-click a related vulnerability to open it, or a source to visit its link. The Physics button on the left tunes the layout and the simulation; the legend at the bottom left hides or shows nodes by kind and by sighting type.
Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
Vulnerability timeline
Sightings and recorded dates, grouped by day · UTC
How durations are calculated
Following the VTEM framework (Black Hat USA 2015), time to patch starts when the vendor or a coordinator was informed, total time to patch at discovery, and disclosure to patch at public disclosure; vendor response time runs from the report to its acknowledgement. Time to exploit and time unpatched start at the earliest discovery or report, falling back to public disclosure. Unpatched time ends at the first recorded patch, or the calculation time when no patch is recorded. Exploitation to patch shows the interval between those two events; a published proof of concept is a public exploit, not exploitation.
Each result shows its source dates. A negative interval means the end event came first; when date-only inputs leave the order open, the result says so. Date-only inputs are approximate. The earliest evidence wins: KEV report dates and sightings are labelled as such. Records describing another vulnerability are listed but never calculated from, and a PoC alone does not establish exploitation. Missing patch evidence does not prove that no patch exists. Filters below change the event list only.
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
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Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.