CVE-2026-54874 in OpenSSL
Summary
by MITRE • 08/25/2026
Issue summary: Receiving a DTLS record for a future epoch while a handshake is in progress causes OpenSSL to buffer far more memory than the record itself requires.
Impact summary: A peer can use a small amount of network traffic to make an OpenSSL DTLS endpoint retain a disproportionately large amount of memory, which may lead to a Denial of Service.
CWE: CWE-405: Asymmetric Resource Consumption (Amplification)
Description: While a DTLS handshake is in progress, a peer may legitimately have already moved on to the next epoch (for example, having sent its ChangeCipherSpec and Finished messages) before the local endpoint has processed the same transition, typically because of reordering on the underlying UDP transport. OpenSSL buffers such early records so that they can be processed once the local endpoint catches up.
Buffering a record currently retains the entire read buffer it arrived in, which is sized to hold the largest possible DTLS record (around 16 kilobytes), rather than just the bytes that make up the record itself. Up to 100 such records may be buffered per connection. As a result, a peer that sends a stream of small forged records claiming to belong to the next epoch can cause an OpenSSL DTLS endpoint to retain around 1.7 megabytes of memory, despite sending only a small fraction of that amount of data over the network.
An attacker therefore gains a memory amplification factor of around 1200, and can multiply the effect across as many associations as it is able to open, making this a remote memory exhaustion Denial of Service risk for DTLS servers. Since the memory retained per connection remains bounded, and any limit an application already places on the number of concurrent associations also bounds the total exposure, this issue has been assessed as Low severity.
FIPS impact: no
No FIPS modules are affected by this issue as the affected code is outside the OpenSSL FIPS module boundary.
OpenSSL 4.0, 3.6, 3.5, 3.4, 3.0, 1.1.1 and 1.0.2 are vulnerable to this issue.
OpenSSL 4.0 users should upgrade to OpenSSL 4.0.2. OpenSSL 3.6 users should upgrade to OpenSSL 3.6.4. OpenSSL 3.5 users should upgrade to OpenSSL 3.5.8. OpenSSL 3.4 users should upgrade to OpenSSL 3.4.7. OpenSSL 3.0 users should upgrade to OpenSSL 3.0.22.
Premium support customers only: OpenSSL 1.1.1 users should upgrade to OpenSSL 1.1.1zi OpenSSL 1.0.2 users should upgrade to OpenSSL 1.0.2zr
This issue was reported on 18 May 2026 by Amazon Web Services. The fix has been developed by Matt Caswell.
-- cut (non-publishing metadata for internal use) -- Reported by: Amazon Web Services Fixed by: Matt Caswell
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Analysis
by VulDB Data Team • 08/25/2026
The vulnerability described involves a significant memory amplification flaw within the Datagram Transport Layer Security implementation of OpenSSL, specifically affecting versions 4.0 through 1.0.2. This issue arises during the DTLS handshake process when an endpoint receives records belonging to a future epoch while still processing earlier stages of the connection establishment. In normal operation, network reordering on UDP transports can cause packets to arrive out of sequence, requiring the protocol implementation to buffer incoming data until it is ready for processing. However, OpenSSL’s current buffering mechanism retains the entire read buffer associated with each record rather than just the specific bytes contained within that record. Since DTLS records are buffered up to a maximum size of approximately sixteen kilobytes per connection, and up to one hundred such buffers can be held simultaneously, this design choice creates an opportunity for disproportionate resource consumption by malicious actors.
An attacker capable of sending small forged packets claiming to belong to the next epoch can exploit this buffering behavior to trigger memory exhaustion on the target system. By transmitting a stream of these minimal-sized records, the adversary forces OpenSSL to allocate and retain large blocks of memory corresponding to the full buffer size for each incoming packet. This results in a memory amplification factor of approximately twelve hundred times the actual network traffic sent by the attacker. Consequently, a relatively small amount of network data can cause an OpenSSL DTLS endpoint to consume around one point seven megabytes of memory per connection. If an attacker is able to open multiple concurrent associations with the vulnerable server, this effect multiplies across all connections, leading to rapid and severe depletion of available system resources.
The operational impact of this vulnerability is a remote Denial of Service condition caused by resource exhaustion. While the memory retained per individual connection remains bounded due to internal limits on buffered records, the cumulative effect across many concurrent sessions can overwhelm server capacity. This aligns with CWE-405, Asymmetric Resource Consumption (Amplification), where an attacker uses minimal resources to cause disproportionate impact on the target infrastructure. The vulnerability is classified as Low severity because existing application-level limits on the number of concurrent connections naturally cap the total exposure, preventing catastrophic system-wide failure in most standard configurations. Nevertheless, for services that allow high volumes of short-lived DTLS sessions or have elevated connection thresholds, this flaw presents a tangible risk to availability and stability.
Mitigation strategies primarily involve upgrading OpenSSL to patched versions where the buffering logic has been corrected to retain only necessary data rather than full buffer allocations. Users running OpenSSL 4.0 should upgrade to version 4.0.2, while those on 3.6, 3.5, 3.4, and 3.0 must update to versions 3.6.4, 3.5.8, 3.4.7, and 3.0.22 respectively. For legacy systems still operating on OpenSSL 1.1.1 or 1.0.2, updates are available through standard channels for newer releases and via premium support subscriptions for the older branches, specifically versions 1.1.1zi and 1.0.2zr. Additionally, administrators can implement network-level controls such as rate limiting on incoming DTLS traffic to mitigate the impact of potential attacks before they reach the application layer. Since this issue lies outside the FIPS module boundary, it does not affect cryptographic compliance but remains critical for maintaining system integrity and availability against resource exhaustion techniques often associated with ATT&CK tactics related to Impact or Resource Hijacking.