Plaintext APPLICATION_DATA injected during TLS handshake delivered to client application post-handshake in ssl

Weakness Type (CWE)

CWE-924 — CWE-924 Improper Enforcement of Message Integrity During Transmission in a Communication Channel

CAPEC

CAPEC-94 — CAPEC-94 Adversary in the Middle (AiTM)

CVSS 4.0 Score

6.3

MEDIUM

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

Vulnerability description

Improper Enforcement of Message Integrity During Transmission in a Communication Channel vulnerability in Erlang/OTP ssl (tls_gen_connection module) allows a network-positioned attacker to inject unauthenticated plaintext that the TLS client application later treats as authenticated server data.

The function tls_gen_connection:handle_protocol_record/3 rejects APPLICATION_DATA records that arrive in pre-handshake states when the TLS endpoint acts as a server, but does not apply the same check when the endpoint acts as a client. A network-positioned attacker can send plaintext APPLICATION_DATA records to the client during the handshake. The records are buffered and, once the handshake completes successfully, delivered to the application as if they were authenticated post-handshake data. The attacker cannot observe the client's response or steer the connection, so the impact is limited to blind injection of unauthenticated bytes. The injection window is wider for TLS versions prior to TLS 1.3 than for TLS 1.3.

This vulnerability is associated with program file lib/ssl/src/tls_gen_connection.erl.

This issue affects OTP from OTP 17.0 before 29.0.3, 28.5.0.3 and 27.3.4.14 corresponding to ssl from 5.3.4 before 11.7.3, 11.6.0.3 and 11.2.12.10. TLS 1.3 is affected starting with OTP 22.0, when TLS 1.3 support was added.

Affected

`pkg:otp/ssl`

Module	Source File	Routine
`tls_gen_connection`	`src/tls_gen_connection.erl`	`tls_gen_connection:handle_protocol_record/3`

Status	Type	Version	Changes / Fixed in
affected	otp ^ⓘ	`5.3.4`	unaffected at `11.7.3` unaffected at `11.6.0.3` unaffected at `11.2.12.10`

`pkg:github/erlang/otp`

Module	Source File	Routine
`tls_gen_connection`	`lib/ssl/src/tls_gen_connection.erl`	`tls_gen_connection:handle_protocol_record/3`

Status	Type	Version	Changes / Fixed in
affected	otp ^ⓘ	`17.0`	unaffected at `29.0.3` unaffected at `28.5.0.3` unaffected at `27.3.4.14`
affected	git ^ⓘ	`84adefa331`	< `07d2d0e93f`

References

https://github.com/erlang/otp/security/advisories/GHSA-gf6r-99xw-6qg6 vendor-advisory related
https://osv.dev/vulnerability/EEF-CVE-2026-54891 related
https://github.com/erlang/otp/commit/07d2d0e93f6aaf7652a81e8df075fc1728da5e96 patch

Credits

Finder: Lukas Backström
Remediation developer: Ingela Anderton Andin
Remediation reviewer: Dan Gudmundsson
Remediation reviewer: Jakub Witczak

CVE record as JSON: GET /cves/CVE-2026-54891.json
OSV record as JSON: GET /osv/EEF-CVE-2026-54891.json