DTLS server cookie bypass during startup window due to empty initial cookie secret

Weakness Type (CWE)

CWE-1394 — CWE-1394 Use of Default Cryptographic Key

CAPEC

CAPEC-485 — CAPEC-485 Signature Spoofing by Key Recreation

CVSS 4.0 Score

6.3

MEDIUM

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

Vulnerability description

Use of Default Cryptographic Key vulnerability in Erlang/OTP ssl (DTLS server) allows predictable DTLS cookie computation during the startup window, enabling source address verification bypass.

On DTLS server startup, dtls_server_connection:initial_hello/3 initializes previous_cookie_secret to the empty binary (<<>>) instead of a random value. Because HMAC with an empty key is deterministic, anyone who observes the plaintext ClientHello can compute dtls_handshake:cookie(<<>>, IP, Port, Hello) and forge a valid DTLS cookie before the first rotation of the cookie secret. The DTLS cookie (RFC 6347 §4.2.1) is a denial-of-service mitigation that prevents spoofed source IPs from forcing the server to allocate state and perform expensive cryptographic operations; it is not an authentication mechanism. During the window from server startup until the first secret rotation (0 to 15 seconds), an attacker who can observe the plaintext ClientHello can bypass the source address verification, enabling DTLS handshake amplification with spoofed source addresses.

This vulnerability is associated with program file lib/ssl/src/dtls_server_connection.erl and program routine dtls_server_connection:initial_hello/3.

This issue affects OTP from OTP 20.0 before 29.0.3, 28.5.0.3 and 27.3.4.14 corresponding to ssl from 8.2 before 11.7.3, 11.6.0.3 and 11.2.12.10.

Affected

`pkg:otp/ssl`

Module	Source File	Routine
`dtls_server_connection`	`src/dtls_server_connection.erl`	`dtls_server_connection:initial_hello/3`

Status	Type	Version	Changes / Fixed in
affected	otp ^ⓘ	`8.2`	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
`dtls_server_connection`	`lib/ssl/src/dtls_server_connection.erl`	`dtls_server_connection:initial_hello/3`

Status	Type	Version	Changes / Fixed in
affected	otp ^ⓘ	`20.0`	unaffected at `29.0.3` unaffected at `28.5.0.3` unaffected at `27.3.4.14`
affected	git ^ⓘ	`e594aad2f8`	< `888e3bcd72`

References

https://github.com/erlang/otp/security/advisories/GHSA-p2m2-3c2w-8jp8 vendor-advisory related
https://osv.dev/vulnerability/EEF-CVE-2026-54887 related
https://github.com/erlang/otp/commit/888e3bcd72d5406016b9e0de741026bc2a6f114d patch

Credits

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

CVE record as JSON: GET /cves/CVE-2026-54887.json
OSV record as JSON: GET /osv/EEF-CVE-2026-54887.json