# CVE-2026-34182 — OpenSSL

> As of 2026-06-10, CVE-2026-34182 is a CRITICAL-severity vulnerability in OpenSSL, CVSS v3.1 9.1, EPSS 1.0% (63.4th percentile). Threadlinqs Intelligence links 2 tracked threat campaigns to CVE-2026-34182, most recently “Microsoft September 2026 Patch Tuesday — 999 CVEs, 3 actively exploited zero-days (CVE-2026-85880, CVE-2026-81963, CVE-2026-85046)”.

**Last updated:** 2026-06-10

## What is CVE-2026-34182?

Issue Summary: Cryptographic Message Services (CMS) processing fails to perform sufficient input validation on the cipher and tag length fields of AuthEnvelopedData containers, leading to various potential compromises. Impact Summary: Attackers making use of these vulnerabilities may achieve key-equivalent functionality for a given CMS recipient and/or bypass integrity validation for a given message. In one use case, an attacker may send a CMS message containing AuthEnvelopedData with the cipher specified as a non-AEAD cipher. OpenSSL erroneously allows this selection, and attempts to decrypt and validate the message. An on-path attacker who captures one legitimate AES-GCM AuthEnvelopedData addressed to the victim can re-emit it with the recipientInfos set left byte-for-byte intact, so the victim's private key still unwraps the genuine CEK (the content-encryption key), but with the inner OID rewritten to AES-256-OFB (Output Feedback Mode, an unauthenticated keystream mode) and with an attacker-chosen IV and ciphertext. The victim initializes AES-256-OFB under the real CEK, never consults the MAC field, and CMS_decrypt() returns success. If the application under attack responds to the attacker with any indicator showing success or failure of the decryption effort, it is possible for the attacker to use this as an oracle to obtain key equivalent functionality for the CEK used for the chosen recipient of the message. In another use case, an attacker can reduce the tag length of the chosen AEAD cipher for a given AuthEnvelopedData container to be a single byte long, allowing an attacker to brute force CMS decryption, producing an integrity bypass for applications that trust CMS_decrypt() to reject modified content. The FIPS modules are not affected by this issue.

The record classifies CVE-2026-34182 under weakness class [CWE-354](https://cwe.mitre.org/data/definitions/354.html). Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs no prior authentication, needs no user interaction, and has high impact on confidentiality, integrity. 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 140 days ago.

## Severity and exploitation probability

- **CVSS v3.1 base score:** 9.1 — CRITICAL (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N`)
- **EPSS (FIRST):** 1.0% probability of exploitation in the next 30 days, higher than 63.4% of all scored CVEs
- **CISA KEV:** Not listed in the CISA Known Exploited Vulnerabilities catalog
- **Threadlinqs priority:** 7.1/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- **Published:** 2026-06-09, last modified 2026-06-10

## Is CVE-2026-34182 being exploited?

It currently carries a trending score of 26 in the Threadlinqs vulnerability feed.

## Affected products and versions

- [OpenSSL](https://intel.threadlinqs.com/vendors/openssl): OpenSSL

## How to fix CVE-2026-34182

No vendor patch reference has been recorded for CVE-2026-34182 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.

## Threat activity tracking CVE-2026-34182

2 tracked threats in the Threadlinqs corpus reference CVE-2026-34182, either in the campaign’s CVE list or as an indicator on the campaign record.

- [Microsoft September 2026 Patch Tuesday — 999 CVEs, 3 actively exploited zero-days (CVE-2026-85880, CVE-2026-81963, CVE-2026-85046)](https://intel.threadlinqs.com/threat/TL-2026-2407) — CRITICAL · 2026-09-08
- [HollowByte: OpenSSL Pre-Authentication TLS DoS Flaw Bloats Server Memory With 11-Byte Payload](https://intel.threadlinqs.com/threat/TL-2026-1457) — MEDIUM · 2026-07-17

## Sources

Enriched from CVE.org, FIRST EPSS, GitHub Security Advisories. Last verified by Threadlinqs on 2026-10-10.

**Vendor advisory and patch**

- [openssl-library.org — vendor advisory](https://openssl-library.org/news/secadv/20260609.txt)
- [github.com — patch](https://github.com/openssl/openssl/commit/9fd97f8cfdc2c0be214998de3b2b55c8edf6c7ac)
- [github.com — patch (439ed7d2c0962ce964482727264668bf277c333f)](https://github.com/openssl/openssl/commit/439ed7d2c0962ce964482727264668bf277c333f)
- [github.com — patch (7947e6a81eb8776802f159fb6762cb7fcf7e34c7)](https://github.com/openssl/openssl/commit/7947e6a81eb8776802f159fb6762cb7fcf7e34c7)
- [github.com — patch (d2ca86bcd43e4f17d899f347101766b6107676e0)](https://github.com/openssl/openssl/commit/d2ca86bcd43e4f17d899f347101766b6107676e0)

_Showing 5 of 6 recorded references._

Canonical: https://intel.threadlinqs.com/cve/CVE-2026-34182
Full detection coverage and IOCs for threats exploiting CVE-2026-34182 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp