# CVE-2026-65634: Superlinear CPU denial of service in Erlang/OTP ASN.1 OBJECT IDENTIFIER decoder

Status: published. Published: 2026-09-22. Updated: 2026-11-11.

Inefficient algorithmic complexity in the Erlang/OTP asn1 OBJECT IDENTIFIER decoder allows a remote unauthenticated attacker to cause denial of service by sending a crafted OID during the TLS handshake.

The BER OID decoder asn1rtt_ber:dec_subidentifiers/3 in lib/asn1/src/asn1rtt_ber.erl and the equivalent PER helper asn1rtt_per_common:dec_subidentifiers/3 in lib/asn1/src/asn1rtt_per_common.erl accumulate a base-128 subidentifier into an unbounded integer using (Av bsl 7) + H per continuation byte. Each shift and addition on the growing accumulator is linear in the number of bits already accumulated, giving quadratic total work in the size of a single subidentifier. The JER helper asn1rtt_jer:json2oid/1 in lib/asn1/src/asn1rtt_jer.erl exhibits the same class of unbounded-integer parsing when decoding a dot-separated OID from JSON. A DER-encoded OBJECT IDENTIFIER with one very large arc (approximately 262 KB of continuation bytes) consumes roughly 13 seconds of CPU on typical hardware.

The vulnerable decoder is generated into every ASN.1 module that contains an OBJECT IDENTIFIER, including OTP-PUB-KEY which is reached during X.509 certificate parsing via public_key:pkix_decode_cert/2. This decoder runs before any signature or trust chain verification, so any Erlang service that parses peer TLS certificates is exposed: the default for TLS clients (which always parse the server certificate) and for mutual-TLS servers (which parse client certificates).

This vulnerability is associated with program files lib/asn1/src/asn1rtt_ber.erl, lib/asn1/src/asn1rtt_per_common.erl and lib/asn1/src/asn1rtt_jer.erl and program routines asn1rtt_ber:dec_subidentifiers/3, asn1rtt_per_common:dec_subidentifiers/3 and asn1rtt_jer:json2oid/1.

This issue affects OTP from OTP 17.0 before OTP 27.3.4.18, OTP 28.5.0.7, and OTP 29.1.1, corresponding to asn1 from 3.0 before 5.3.4.3, 5.4.3.1, and 5.5.2. Whether OTP before OTP 17.0, corresponding to asn1 before 3.0, is affected is unknown.

## Remediation

- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: EEF) — https://github.com/erlang/otp/commit/0fe2c02fdc06fab1c63be9db1a7456993d20f838

## Affected products and versions

- Erlang / OTP (otp): ≥ 17.0; < * (affected, otp); unaffected at 27.3.4.18; unaffected at 28.5.0.7; unaffected at 29.1.1. Source: CNA: EEF
- Erlang / OTP (asn1): ≥ 3.0; < * (affected, otp); unaffected at 5.3.4.3; unaffected at 5.4.3.1; unaffected at 5.5.2. Source: CNA: EEF
- Erlang / OTP (erlang/otp): ≥ 84adefa331c4159d432d22840663c38f155cd4c1; < 0fe2c02fdc06fab1c63be9db1a7456993d20f838 (affected, git); ≥ 0fe2c02fdc06fab1c63be9db1a7456993d20f838; < * (unaffected, git). Source: CNA: EEF

## Severity and prioritization

- CVSS 4.0: 8.2 (high); CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N; source: CNA: EEF

- CISA KEV: No listing in collected sources

- EPSS: 0.27% as of 2026-11-10; percentile 18.65%

- SSVC: exploitation none; automatable yes; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-407

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/erlang/otp/security/advisories/GHSA-qghx-23m5-r55m (CNA: EEF; related, vendor-advisory)

- https://cna.erlef.org/cves/CVE-2026-65634.html (CNA: EEF; related)

- https://osv.dev/vulnerability/EEF-CVE-2026-65634 (CNA: EEF; related)

- https://www.erlang.org/doc/system/versions.html#order-of-versions (CNA: EEF; x_version-scheme)

- https://github.com/erlang/otp/commit/0fe2c02fdc06fab1c63be9db1a7456993d20f838 (CNA: EEF; patch)

## Provenance

- CNA: EEF: https://www.cve.org/CVERecord?id=CVE-2026-65634; retrieved 2026-11-11; source updated 2026-11-11

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-65634; retrieved 2026-11-11; source updated Not reported

Revision: 941d20d90a48b218bf5a23de69dd6346b2e3d52d9245b118d6926e3865feb6f5

Canonical: https://y2.dev/cve/CVE-2026-65634

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