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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.
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OpenSSL published an analysis of the HollowByte report, arguing the issue was bounded to roughly 128 KiB per connection and that observed outages were primarily due to slowloris-style stalled connections and allocator behavior rather than unbounded memory exhaustion. The project said it treated the change as a hardening fix rather than a CVE-worthy vulnerability and advised operators to upgrade and enforce connection timeouts and limits.
OpenSSL addressed the HollowByte issue by changing buffer handling to incremental growth and released fixes in version 4.0.1 with backports to 3.6.3, 3.5.7, 3.4.6, and 3.0.21. One report notes the fix was issued without a CVE assignment.
Okta's Red Team identified a denial-of-service vulnerability dubbed HollowByte in OpenSSL, where an 11-byte malicious TLS handshake can trigger attacker-controlled memory pre-allocation and persistent memory growth on affected systems.
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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**.
Aug 6, 2026
Researchers publicly disclosed **HTTP/2 Bomb**, a remote denial-of-service technique that abuses standard HTTP/2 behavior to rapidly exhaust memory on major web servers and proxies, including **nginx, Apache HTTP Server, Microsoft IIS, Envoy, and Cloudflare Pingora**. The attack combines **HPACK header-compression amplification** with a **Slowloris-style flow-control stall**, letting a low-bandwidth client trigger disproportionate server-side allocations and keep that memory pinned by advertising a zero-byte window. Reports said a single machine on a 100 Mbps connection could make vulnerable services inaccessible within seconds, with testing showing **Apache httpd** and **Envoy** consuming roughly **32 GB of RAM** in about **10 to 20 seconds** under default HTTP/2 configurations. Public disclosures and proof-of-concept code indicated the amplification largely comes from per-header bookkeeping rather than oversized decoded header values, allowing common decoded-size limits to be bypassed. **Apache** tracked its exposure as **`CVE-2026-49975`** and released a fix in **`mod_http2 2.0.41`**, while **nginx** addressed the issue in **`1.29.8`**; advisories initially said **IIS, Envoy, and Pingora** lacked patches, though later disclosures showed **Envoy** assigned **`CVE-2026-47774`** and published an advisory. Researchers estimated more than **880,000** internet-exposed HTTP/2 systems could be affected and recommended upgrading where fixes exist, or otherwise disabling HTTP/2, enforcing strict header-count limits, and monitoring for abnormal memory growth.
Jul 20, 2026
OpenSSL disclosed **Heartbleed** (`CVE-2014-0160`), a critical flaw in the TLS/DTLS heartbeat extension caused by a missing bounds check that let remote attackers read up to **64 KB** of memory from vulnerable clients and servers. The bug affected OpenSSL `1.0.1` through `1.0.1f` and some `1.0.2-beta` releases, potentially exposing private keys, passwords, cookies, and other sensitive data without leaving reliable forensic traces. OpenSSL urged organizations to upgrade to `1.0.1g` or disable heartbeats if they could not patch immediately, while researchers and vendors warned that remediation also required rotating keys, revoking and reissuing certificates, and resetting passwords only after affected services had been fixed. The vulnerability triggered emergency responses across the Internet and in embedded infrastructure, with Cisco, Juniper, Western Digital, Apple, Android device makers, and major online platforms assessing or patching affected products. Reports showed the risk extended beyond websites to routers, VPNs, storage appliances, mobile devices, and other systems using embedded OpenSSL, while Cloudflare demonstrated that theft of SSL private keys was practically achievable and incident reporting linked the flaw to real-world compromise, including theft of Canadian taxpayer data and suspected corporate intrusions. The incident also exposed a structural weakness in Internet security: one of the web’s most widely trusted cryptographic libraries had been maintained by a small, underfunded team, prompting calls for sustained investment in critical open-source infrastructure.
Jun 29, 2026