# CVE-2026-54876 — OpenSSL

> As of 2026-08-05, CVE-2026-54876 is a HIGH-severity vulnerability in OpenSSL, CVSS v3.1 7.5, EPSS 0.5% (42.7th percentile). Threadlinqs Intelligence links 1 tracked threat campaign to CVE-2026-54876, most recently “CVE-2026-54876 — OpenSSL Client-Side Memory Leak in OCSP Response Checking (Denial of Service)”.

**Last updated:** 2026-08-05

## What is CVE-2026-54876?

Issue summary: A malicious TLS server can cause a memory leak in a TLS client that has enabled OCSP response checking by sending an OCSP response that contains no single response entries. Impact summary: An attacker can leak an attacker-tunable amount of memory per TLS handshake in a victim client application. A long-running client that repeatedly connects to a malicious server can have its memory exhausted, resulting in a Denial of Service. CWE: CWE-401: Missing Release of Memory after Effective Lifetime Description: The affected function is called during X.509 certificate chain verification when OCSP response checking is enabled with the X509_V_FLAG_OCSP_RESP_CHECK or X509_V_FLAG_OCSP_RESP_CHECK_ALL verification flags, for example when a TLS client verifies an OCSP response stapled into the TLS handshake by the server. When the received BasicOCSPResponse contains an empty SEQUENCE OF SingleResponse, which is permitted on the wire and accepted by the OpenSSL decoder, the OCSP_BASICRESP structure allocated by OCSP_response_get1_basic() was not freed because an early return bypassed the cleanup code at the end of the function. The amount of memory leaked per handshake can be amplified by the attacker by padding the certs field of the BasicOCSPResponse with bogus certificates, which are parsed and stored in the leaked structure before the empty response check triggers the early return. A long-running TLS client that repeatedly connects to a malicious server can have its memory exhausted over time. OCSP response checking is not enabled by default. Only client applications that explicitly enable the OCSP response check verification flags are affected. FIPS impact: no The FIPS modules in 4.0 and 3.6 are not affected by this issue as the affected code is outside the OpenSSL FIPS module boundary.

The record classifies CVE-2026-54876 under weakness class [CWE-401](https://intel.threadlinqs.com/cwe/CWE-401). 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 availability. 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 83 days ago.

## Severity and exploitation probability

- **CVSS v3.1 base score:** 7.5 — HIGH (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **EPSS (FIRST):** 0.5% probability of exploitation in the next 30 days, higher than 42.7% of all scored CVEs
- **CISA KEV:** Not listed in the CISA Known Exploited Vulnerabilities catalog
- **Threadlinqs priority:** 5.5/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- **Published:** 2026-08-05

## Is CVE-2026-54876 being exploited?

It currently carries a trending score of 29 in the Threadlinqs vulnerability feed.

## Affected products and versions

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

## How to fix CVE-2026-54876

No vendor patch reference has been recorded for CVE-2026-54876 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-2026-54876

1 tracked threat in the Threadlinqs corpus references CVE-2026-54876, either in the campaign’s CVE list or as an indicator on the campaign record.

- [CVE-2026-54876 — OpenSSL Client-Side Memory Leak in OCSP Response Checking (Denial of Service)](https://intel.threadlinqs.com/threat/TL-2026-1909) — HIGH · 2026-08-06

## Sources

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

**Vendor advisory and patch**

- [openssl-library.org — vendor advisory](https://openssl-library.org/news/secadv/20260805.txt)
- [github.com — patch](https://github.com/openssl/openssl/commit/d8c51048ac037a21bae0f41cad7a3920dc7f3638)
- [github.com — patch (155b5fe0f93365e6df1c56ee3606b121080c6c12)](https://github.com/openssl/openssl/commit/155b5fe0f93365e6df1c56ee3606b121080c6c12)

Canonical: https://intel.threadlinqs.com/cve/CVE-2026-54876
Full detection coverage and IOCs for threats exploiting CVE-2026-54876 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp