Live Exposure Defense: From CVE to Confirmed Exposure in 12 Hours – See more

Back
New CVE Detected

CVE-2026-65634 – Denial of Service (TLS Handshake CPU Exhaustion) – Erlang/OTP asn1 (OTP 17.0–29.1.0

Be the first to know when new zero-days emerge:

Subscribe to Email Alerts
Subscribe to RSS Feed

Summary

CVE-2026-65634 is a denial-of-service vulnerability in the ASN.1 OBJECT IDENTIFIER (OID) decoder shipped with Erlang/OTP’s asn1 module. The decoder uses an algorithm with quadratic time complexity when parsing a single very large base-128 subidentifier, allowing a remote, unauthenticated attacker to exhaust CPU on a target by sending a crafted OID — most notably inside an X.509 certificate presented during a TLS handshake. The issue carries a CVSS score of 8.2 (High).

Technical details

  • Root cause: The decoder routines asn1rtt_ber:dec_subidentifiers/3 (BER), asn1rtt_per_common:dec_subidentifiers/3 (PER), and asn1rtt_jer:json2oid/1 (JER) accumulate each base-128 continuation byte into an unbounded integer via repeated bit-shift-and-add operations. Because each operation’s cost grows with the number of bits already accumulated, decoding a single long subidentifier is quadratic in its length rather than linear.
  • Trigger conditions: A DER/PER-encoded OBJECT IDENTIFIER containing one abnormally large arc (encoded as a long run of base-128 continuation bytes, roughly 262 KB) triggers the excessive computation; on typical hardware this can consume on the order of 13 seconds of CPU per decode.
  • Attack vector: Network. The generated OID decoder is embedded in every ASN.1 module that includes an OBJECT IDENTIFIER, including OTP-PUB-KEY, which is used during X.509 certificate parsing (public_key:pkix_decode_cert/2). This code path executes before signature or trust-chain verification, so any Erlang process that parses a peer’s TLS certificate — TLS clients by default, and mutual-TLS servers with peer verification enabled — can be forced to decode an attacker-supplied malicious certificate.
  • Impact: Repeated requests containing crafted OIDs/certificates can exhaust server CPU, degrading or denying service for the affected Erlang node and any application built on it (e.g., messaging brokers, XMPP servers) that terminates TLS with peer certificate verification.

Affected software

  • Erlang/OTP 17.0 up to (but not including) 27.3.4.18
  • Erlang/OTP 28.0 up to (but not including) 28.5.0.7
  • Erlang/OTP 29.0 up to (but not including) 29.1.1
  • asn1 module 3.0 up to (but not including) 5.3.4.3, 5.4.3.1, or 5.5.2 respectively

Severity

CVSS v4.0 Base Score: 8.2 (High)
Vector: 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

Mitigation and recommended actions

  • Immediate: Upgrade Erlang/OTP to 27.3.4.18, 28.5.0.7, or 29.1.1 (or update the standalone asn1 module to 5.3.4.3, 5.4.3.1, or 5.5.2, matching your OTP release line).
  • If patching is not immediately possible: No workaround exists that fully eliminates the exposure. Since the vulnerable code path is only reached when a peer certificate is decoded, limiting exposure to untrusted TLS peers (e.g., restricting which clients can complete a TLS handshake with verify_peer enabled, or placing the service behind network-level filtering) can reduce risk until the upgrade is applied.

References

Are you exposed?

Get a free report of your organization’s exposure to this CVE and threat

  • Mapping of all Assets with this Technology
  • Identification of potentially exposed assets to this CVE
  • Confirmation of verified exploitable assets
Get Exposure Report

How IONIX’s External Exposure Management Platform Detects and Validates
Zero-Days to Shrink MTTR

1

Map your entire attack surface (continously)

IONIX uses multi-factor discovery methods, including DNS analysis, certificate mapping, metadata inspection, and more, to automatically map every internet-facing asset across your environment. This includes cloud instances, third-party platforms, shadow IT, and even forgotten infrastructure that traditional tools miss.

2

Monitor for new CVEs

Dozens of threat intel feeds using agentic technology are continuously analyzed to detect the appearance of proof-of-concept code, exploit kits, and indicators of active targeting. IONIX goes further by applying AI to proactively evaluate whether emerging vulnerabilities are likely to be exploited, even before PoCs go public.

3

Identify Potential External Exposures

Not all CVEs matter. IONIX filters vulnerabilities by asking attacker-centric questions: Can it be reached from the internet? Does it require authentication? Is it being exploited in the wild? This dramatically reduces noise and focuses teams on threats that can actually be weaponized.

4

Create Safe, Scalable Exploit Validations

IONIX transforms real-world PoCs into safe, non-intrusive test payloads that can be run in production environments without disruption. These simulations are precisely targeted to the systems that are vulnerable, ensuring rapid validation without unnecessary load.

5

Execute Exploit Validations

By combining context about software stack, versioning, exposure status, and reachability, IONIX ensures that only the right payloads are executed against the right assets, maximizing efficiency and minimizing risk.

6

Drive Fast and Actionable Remediation

Results are routed through integrations with ticketing, SOAR, and SIEM tools. Issues are written in plain language, bundled into remediation clusters, and prioritized based on asset criticality, exploitability, and blast radius. This shortens mean time to remediation (MTTR) and empowers teams to act with confidence.

Are you exposed?

Get a free report of your organization’s exposure to this CVE and threat

  • Mapping of all Assets with this Technology
  • Identification of potentially exposed assets to this CVE
  • Confirmation of verified exploitable assets
Get Exposure Report
Close

Subscribe to Threat Center RSS

Copy/paste the link below into your preferred RSS reader or follow these instructions to subscribe to Slack alerts.

Open RSS feedSlack setup instructions

Close

Get Real-Time CVE Alerts to Your Email

Be the first to know when new zero-days emerge