CVE-2026-84782

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.

Affected Software

VendorProductVersion RangeStatus
OpenSSLOpenSSL4.0.0 < 4.0.3affected
OpenSSLOpenSSL3.6.0 < 3.6.5affected
OpenSSLOpenSSL3.5.0 < 3.5.9affected
OpenSSLOpenSSL3.4.0 < 3.4.8affected
OpenSSLOpenSSL3.0.0 < 3.0.23affected
OpenSSLOpenSSL1.1.1 < 1.1.1zjaffected
OpenSSLOpenSSL1.0.2 < 1.0.2zsaffected

Weaknesses

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

ADP Enrichment

CISA ADP Vulnrichment

  • SSVC:
  • Exploitation: none
    • Automatable: yes
    • Technical Impact: partial

References