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

Quick assessment

Affected
OpenSSL OpenSSL
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

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 suspende

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I. Basic Information for CVE-2026-84782

Vulnerability Information

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Vulnerability Title
DTLS Retransmits Handshake Messages From a Stale Buffer Offset
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
N/A
Source: CVE Program / CVE List V5
Vulnerability Type
跨界内存读
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
OpenSSL OpenSSL 4.0.0 ~ 4.0.3 -

II. Public POCs for CVE-2026-84782

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III. Intelligence Information for CVE-2026-84782

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Other References for CVE-2026-84782 (5)

Same Patch Batch · OpenSSL · 2026-09-29 · 14 CVEs total

CVE-2026-35189 Excessive Memory Allocation in Relative CRLDP Processing
CVE-2026-35191 QUIC Unvalidated Amplification Credit may be Over Accounted
CVE-2026-75806 Unauthenticated and Undersized DTLS 1.2 AEAD Record Causes DoS
CVE-2026-75804 QUIC Connection-Level Flow Control is Not Enforced for Streams
CVE-2026-75805 NULL Pointer Dereference in CMP Client Revocation Response Handling
CVE-2026-42772 Potential CPU DoS via O(n^2) Fragment Reassembly in QUIC
CVE-2026-54873 QUIC STREAM Fragment Metadata DoS
CVE-2026-54872 Timing Side-Channel in Scalar Multiplication for Non-NIST EC Curves
CVE-2026-54875 Non-Constant-Time SM2 Scalar Multiplication on ARM64 and RISC-V
CVE-2026-77696 Timing Side-Channel in SM2 Signature Generation
CVE-2026-72897 Out-of-Bounds Access After SSL_set_SSL_CTX() During a Handshake
CVE-2026-84784 QUIC: Unbounded RETIRE_CONNECTION_ID Backlog
CVE-2026-84783 Use-After-Free in X.509 Extension Cache Under Concurrent Use

IV. Related Vulnerabilities

Same product: OpenSSL
Same vendor: OpenSSL
Same weakness: CWE-125

V. Comments for CVE-2026-84782

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