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OpenSSL disclosed CVE-2026-54876, a low-severity flaw that lets a malicious TLS server trigger a client-side memory leak during OCSP response checking. The bug appears when a TLS client has explicitly enabled OCSP validation and processes a BasicOCSPResponse with an empty SingleResponse sequence, leaving an allocated OCSP_BASICRESP structure unfreed. By repeating handshakes and tuning the leaked memory per connection, an attacker could exhaust memory in long-running client applications and cause a denial of service.
The issue affects OpenSSL 4.0 and 3.6 but not 3.5, 3.4, 3.0, 1.1.1, or 1.0.2, and OpenSSL said its FIPS modules are not impacted because the vulnerable code sits outside the FIPS boundary. The fix changes check_cert_ocsp_resp() in crypto/x509/x509_vfy.c so error handling routes through cleanup and frees the OCSP basic response instead of returning early; patches are already available in commits d8c5104 and 155b5fe and are slated for inclusion in releases 4.0.2 and 3.6.4.
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OpenSSL disclosed CVE-2026-54876 as a low-severity client-side memory leak in OCSP response checking that a malicious TLS server could trigger when clients explicitly enabled OCSP response verification. The advisory said OpenSSL 4.0 and 3.6 were affected, while several earlier branches were not, and recommended upgrading once fixed releases become available.
OpenSSL published code commits 155b5fe and d8c5104 that changed check_cert_ocsp_resp() to route empty OCSP BasicResponse handling through cleanup, preventing the OCSP_BASICRESP object from leaking. These commits made the fixes available in the Git repository ahead of release versions 3.6.4 and 4.0.2.
OpenSSL said Zhenzhe Shao independently reported the same OCSP response checking memory leak later in June. The eventual fix was developed by Mounir Idrassi.
OpenSSL said Bhabani Sankar Das reported the issue that became CVE-2026-54876. The flaw involved a client-side memory leak in OCSP response checking.
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OpenSSL disclosed a broad set of vulnerabilities affecting ASN.1 parsing, PKCS#12, CMS/PKCS#7, QUIC, OCSP, CMP/CRMF, DH key validation, AEAD cipher handling, and certificate and email validation across the 4.0, 3.6, 3.5, 3.4, and 3.0 branches. The most severe issue, **CVE-2026-45447**, is a high-severity heap use-after-free in `PKCS7_verify()` that can be triggered by specially crafted PKCS#7 or S/MIME signed messages and could lead to crashes, heap corruption, or potentially remote code execution. The advisory also details moderate-severity flaws that could enable forged CMS `AuthEnvelopedData` messages, denial-of-service conditions in QUIC and OCSP processing, a TLS client double-free via OCSP stapling, a QUIC server `NULL` dereference, and cryptographic failures in AES-OCB when applications use the `EVP_Cipher()` one-shot API, alongside numerous lower-severity parsing, validation, and bounds-checking bugs. OpenSSL said most issues were fixed in **4.0.1**, **3.6.3**, **3.5.7**, **3.4.6**, and **3.0.21**, with **1.1.1zh** and **1.0.2zq** issued for supported legacy customers; most flaws were reported as outside the OpenSSL FIPS module boundary, except **CVE-2026-42770**, which affects FIPS modules in multiple supported branches.
Jun 29, 2026
Okta's Red Team disclosed **HollowByte**, a denial-of-service flaw in OpenSSL that lets a remote, unauthenticated attacker send a malicious TLS handshake as small as **11 bytes** and trigger excessive memory allocation. The issue affects older OpenSSL versions that trust an attacker-controlled handshake length and pre-allocate buffers before validating the full payload, allowing repeated requests to block worker threads and drive up memory consumption on exposed services such as **NGINX**. Researchers said repeated exploitation with randomized claimed sizes can cause severe heap fragmentation in `glibc`, leading to persistent resident memory growth even after connections close and, in testing, leaving systems vulnerable to **OOM** conditions or large amounts of locked-up memory while staying below normal connection limits. OpenSSL fixed the bug by switching to incremental buffer growth and backported the change to supported branches, with patched releases available in **4.0.1**, **3.6.3**, **3.5.7**, **3.4.6**, and **3.0.21**; defenders are being urged to upgrade promptly despite the flaw not receiving a CVE.
Jul 24, 2026
OpenSSL released fixes for seven vulnerabilities across multiple supported branches, led by **CVE-2026-31790**, a Moderate-severity flaw in RSA KEM `RSASVE` encapsulation that can leak stale or uninitialized memory to a malicious peer. The issue can be triggered when applications process attacker-supplied invalid RSA public keys without validating them first. The advisory also disclosed six Low-severity bugs: an AVX-512/VAES-specific out-of-bounds read in AES-CFB-128, a potential use-after-free or double-free in DANE client code, two CMS-related NULL pointer dereferences, a delta CRL NULL dereference, and a heap buffer overflow in hexadecimal conversion on 32-bit platforms. The project advised users to upgrade to fixed releases **3.0.20**, **3.3.7**, **3.4.5**, **3.5.6**, and **3.6.2**, with premium-support fixes available for **1.1.1zg** and **1.0.2zp** where applicable. OpenSSL said branches **3.1** and **3.2** are out of support and were not analyzed, leaving organizations running those versions without reviewed fixes in this advisory.
Jun 29, 2026