# CVE-2026-54876: Client-Side Memory Leak in OCSP Response Checking

> A malicious TLS server can cause memory exhaustion in clients with OCSP checking enabled, leading to denial of service.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 5 Aug 2026
- **Updated:** 5 Aug 2026
- **Also known as:** CLEANSTART-2026-WR38385, DEBIAN-CVE-2026-54876, GHSA-5cfw-78wc-wvjq, RHSA-2026:57021, UBUNTU-CVE-2026-54876

## What is CVE-2026-54876?

CVE-2026-54876 is a high-severity denial of service vulnerability in OpenSSL, published on 5 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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.

Weakness: CWE-401 (Missing Release of Memory after Effective Lifetime)

## Which versions are affected by CVE-2026-54876?


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `openssl3` | Red Hat:hummingbird:1 | All versions | 0:3.5.7-2.2.hum1 |
| `openssl3-devel` | Red Hat:hummingbird:1 | All versions | 0:3.5.7-2.2.hum1 |
| `openssl3-devel-engine` | Red Hat:hummingbird:1 | All versions | 0:3.5.7-2.2.hum1 |
| `openssl3-libs` | Red Hat:hummingbird:1 | All versions | 0:3.5.7-2.2.hum1 |

## How do I fix CVE-2026-54876?

Apply the vendor's patch.

## Is CVE-2026-54876 being exploited?

There is no known exploitation of CVE-2026-54876 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-54876 and fix it if it is affected.

What it is: CVE-2026-54876 is a high-severity denial of service vulnerability in OpenSSL, published on 5 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-54876 in the wild and no public exploit code.

Affected product: OpenSSL. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-54876/ (Markdown: https://insights.sbomify.com/CVE-2026-54876/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-54876
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-54876
- OSV: https://osv.dev/vulnerability/CVE-2026-54876

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-54876/
Summaries are generated and may contain mistakes; the official description above is the record.