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Response snapshot Oct 27, 2026, 16:01 UTC

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VulnerabilityGHSA-2mjx-qc3c-rqvc

Rustls: TLS 1.3 handshake messages incorrectly accepted across encryption level boundaries

Rustls accepted TLS 1.3 handshake messages sent at the wrong encryption level when they followed a key-changing message in the same record.

Published Updated

At a glance

Exploited
Not known
Severity
Not scored yet
Chance of exploitation
Not estimated
Sources
1 source

What to do

GitHub lists first patched versions: rustls: 0.23.45. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-2mjx-qc3c-rqvc (opens a new tab)

What happened

Rustls accepted TLS 1.3 handshake messages sent at the wrong encryption level when they followed a key-changing message in the same record. The handshake transcript is still authenticated, so a network-position attacker cannot use this to alter or complete a handshake; the practical effect is that a peer could send handshake messages that should be encrypted in plaintext without rustls rejecting the connection.

This issue affects rustls versions 0.23.13 through 0.23.44 inclusive.

# Original report ### Summary Rustls (tested version 0.23.44, and it appears still an issue on latest master though I have not tested this) accepts a TLS 1.3 server flight where a plaintext EncryptedExtensions is packed into the same record as the ServerHello.

This is very similar to Go's CVE-2025-61730 fixed in https://github.com/golang/go/commit/5046bdf8a612b35a2c1a9e168054c1d5c65e7dd7

Continue reading

### Details It appears `Deframer::aligned` considers itself aligned as long as all messages remaining in the buffer are complete. Rustls processes the ServerHello, installs the handshake keys, then pulls the complete (plaintext) EncryptedExtensions out of the buffer.

This is insufficient per RFC 8446 section 5.1's

> Handshake messages MUST NOT span key changes. Implementations MUST verify that all messages immediately preceding a key change align with a record boundary; if not, then they MUST terminate the connection with an "unexpected_message" alert. Because the ClientHello, EndOfEarlyData, ServerHello, Finished, and KeyUpdate messages can immediately precede a key change, implementations MUST send these messages in alignment with a record boundary.

### Impact An on path attacker can inject plaintext messages that are accepted.

### Tool Use Disclosure This was discovered by a new TLS/DTLS test suite currently under construction. The specific testcase was inspired by the Go CVE. Other tested implementations (Botan, OpenSSL, BoringSSL, Go, wolfSSL) reject this protocol flow. Daybreak Blue reviewed the rustls code to identify probable root cause.

Affected package ranges reported by GitHub: rustls: >= 0.23.13, < 0.23.45

Related technology

Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-2mjx-qc3c-rqvc (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-2mjx-qc3c-rqvc, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, October 27). Rustls: TLS 1.3 handshake messages incorrectly accepted across encryption level boundaries. https://kevwire.com/record/GHSA-2mjx-qc3c-rqvc

MLA

"Rustls: TLS 1.3 handshake messages incorrectly accepted across encryption level boundaries." KEVWire, 27 Oct. 2026, kevwire.com/record/GHSA-2mjx-qc3c-rqvc.

Chicago

KEVWire. "Rustls: TLS 1.3 handshake messages incorrectly accepted across encryption level boundaries." Last modified October 27, 2026. https://kevwire.com/record/GHSA-2mjx-qc3c-rqvc.

Evidence summary (plain text)

Rustls: TLS 1.3 handshake messages incorrectly accepted across encryption level boundaries (Oct 5, 2026).
Rustls accepted TLS 1.3 handshake messages sent at the wrong encryption level when they followed a key-changing message in the same record. The handshake transcript is still authenticated, so a network-position attacker cannot use this to alter or complete a handshake; the practical effect is that a peer could send handshake messages that should be encrypted in plaintext without rustls rejecting the connection.

This issue affects rustls versions 0.23.13 through 0.23.44 inclusive.
Sources:
GitHub-reviewed advisory GHSA-2mjx-qc3c-rqvc: https://github.com/advisories/GHSA-2mjx-qc3c-rqvc
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc
Record ID: GHSA-2mjx-qc3c-rqvc.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Oct 27, 2026, 16:00 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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