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.
What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)
The EG score (7.5): severity, escalated by confirmed exploitation. This CVE's 7.5 is its impact severity (EG Severity), not escalated.
- EG Severity
- 7.5 HIGHCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.GitHub Security Advisory CVSS
- EG Likelihood
- 0.5% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-10-29). FIRST's exploitation probability, not an EchelonGraph model.
- Confirmed exploitation
- None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
- EG Priority
- SSVC Track at medium mission impactTrack at low or medium mission impact; Attend at high (mission-essential systems).CISA BOD 26-04: 14 days if the affected system is publicly exposed; 60 days if it is not.Each input and its source, and whom BOD 26-04 binds: the SSVC and BOD 26-04 blocks below.
SSVC (CISA's decision table, applied by EchelonGraph)Track at low or medium mission impact; Attend at high (mission-essential systems).
A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.
Exploitation none (CISA Vulnrichment) · Automatable yes (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table
BOD 26-04 (CISA's remediation timeline, Table 1)14 days if the affected system is publicly exposed; 60 days if it is not.
The score's inputs: In CISA KEV no (CISA's KEV catalog) · Automatable yes (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it