EUVD-2026-119372Published

Rustls 0.23.13 before 0.23.45 TLS 1.3 Handshake Encryption Level Bypass

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cve-program · CVE-2026-123613

Published

Rustls from 0.23.13 before 0.23.45 accepts TLS 1.3 handshake messages at the wrong encryption level when they follow a key-changing message in the same record, because Deframer::aligned does not enforce RFC 8446 record-boundary alignment. A peer or on-path attacker can pack a plaintext EncryptedExtensions with the ServerHello, which rustls accepts unencrypted.

Source published: 8 Nov 2026 01:38:37 UTC
Source modified: 10 Nov 2026 17:56:44 UTC
Saved here: 10 Nov 2026 19:21:22 UTC
Source terms: CVE Program Terms of Use

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CVSS 4.0 · 6.9 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N

CVSS 3.1 · 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

euvd · EUVD-2026-119372

Published

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EUVD source date text has no stated timezone and is retained without inventing a UTC instant. Related bulletin membership is not an alias, common cause or applicability claim. A missing vector with a zero score is treated as unrated. Complete vendor/product and underlying source evidence remains in the original JSON.

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datePublished: Nov 8, 2026, 1:38:37 AM

dateUpdated: Nov 10, 2026, 5:56:44 PM

1 related source bulletins · separate from aliases

msrc_CVE-2026-123613: Rustls 0.23.13 before 0.23.45 TLS 1.3 Handshake Encryption Level Bypass

CVE-2026-123613

Source published: Nov 8, 2026, 1:38:37 AM (timezone not stated)
Source modified: Nov 10, 2026, 5:56:44 PM (timezone not stated)
Saved here: 14 Nov 2026 11:58:47 UTC
Source terms: ENISA EUVD · source terms and attribution apply

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EUVD CVSS 4.0 · 6.9 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N

nvd · CVE-2026-123613

Published

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Source analysis status: Awaiting Analysis

Weakness classifications: CWE-20

Original publisher date fields

published: 2026-11-08T02:16:56.780

lastModified: 2026-11-12T20:28:31.817

Source published: 8 Nov 2026 02:16:56 UTC
Source modified: 12 Nov 2026 20:28:31 UTC
Saved here: 14 Nov 2026 12:57:57 UTC
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CVSS 4.0 · [email protected] · Secondary · 6.9 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

CVSS 3.1 · [email protected] · Secondary · 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

osv · GHSA-2mjx-qc3c-rqvc

Published

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 ### 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.

Source published: 5 Oct 2026 23:30:17 UTC
Source modified: 8 Nov 2026 10:55:54 UTC
Saved here: 8 Nov 2026 11:07:08 UTC
Source terms: GitHub Advisory Database · CC-BY-4.0

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CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

Publisher rating · MODERATE

osv · RUSTSEC-2026-0285

Published

Rustls accepted TLS 1.3 handshake messages sent at the wrong encryption level when they followed a key-changing message in the same record. For example, a plaintext `EncryptedExtensions` message packed into the same record as the `ServerHello` was accepted. RFC 8446 section 5.1 requires that handshake messages do not span key changes, and that implementations terminate the connection with an "unexpected_message" alert if they do. 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 is functionally the same bug as Go's [GO-2026-4340](https://pkg.go.dev/vuln/GO-2026-4340) (CVE-2025-61730).

Source published: 14 Sep 2026 12:00:00 UTC
Source modified: 9 Nov 2026 09:21:20 UTC
Saved here: 9 Nov 2026 10:04:30 UTC
Source terms: OSV · upstream source license applies

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CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N