VulnerabilityPublished 29 Sep 2026Updated 10 Nov 2026

CVE-2026-77696: OpenSSL · Timing Side Channel

Affects OpenSSLSource CVE Database V5

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Not known to be exploited · CVSS 3.7 Low · fixed in 4.0.3 : update OpenSSL when convenient.

Data as of 10 Nov 2026, 13:17 UTC

CVSS 3.1 base score

3.7Low

How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

One scorer or none

CVSS scores by source
CISA-ADP	CVSS 3.1	3.7

Exploitation: No evidence of active exploitation and no public proof of concept
Automatable: Attackers cannot reliably automate steps 1–4 of the kill chain
Technical impact: Limited control over the software or limited information exposure

CISA SSVC assessment, 2026-09-29.

Patch

Available – fixed in 4.0.3, 3.6.5, 3.5.9 +3

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N

Attack Vector: Network
Attack Complexity: High
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: Low
Integrity: None
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: High: A successful attack depends on conditions beyond the attacker's control. That is, a successful attack cannot be accomplished at will, but requires the attacker to invest in some measurable amount of effort in preparation or execution against the vulnerable component before a successful attack can be expected. For example, a successful attack may require an attacker to: gather knowledge about the environment in which the vulnerable target/component exists; prepare the target environment to improve exploit reliability; or inject themselves into the logical network path between the target and the resource requested by the victim in order to read and/or modify network communications (e.g., a man in the middle attack).
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 29 Sep 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 10 Nov 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

Product	Affected	Fixed in
OpenSSLOpenSSL	Affected >=4.0.0 <4.0.3	Fixed in 4.0.3
OpenSSLOpenSSL	Affected >=3.6.0 <3.6.5	Fixed in 3.6.5
OpenSSLOpenSSL	Affected >=3.5.0 <3.5.9	Fixed in 3.5.9
OpenSSLOpenSSL	Affected >=3.4.0 <3.4.8	Fixed in 3.4.8
OpenSSLOpenSSL	Affected >=3.0.0 <3.0.23	Fixed in 3.0.23
OpenSSLOpenSSL	Affected >=1.1.1 <1.1.1zj	Fixed in 1.1.1zj

AI-suggested

Fixed versions of OpenSSL are available: 4.0.3, 3.6.5, 3.5.9, 3.4.8, 3.0.23, and 1.1.1zj. Users should upgrade to these versions or later to remediate the vulnerability. No additional mitigations or workarounds are specified. Since this is a cryptographic timing side-channel, patching is the recommended and effective mitigation.

Description

CVE-2026-77696 is a timing side-channel vulnerability in OpenSSL's SM2 signature generation. The signature computation uses variable-time arithmetic on secret values, allowing an attacker who can measure signing times to gain information about the secret nonce. Over many signatures, this can lead to private key recovery via lattice or Hidden Number Problem attacks. This affects all platforms running vulnerable OpenSSL versions. The vulnerability has a low CVSS score and does not impact FIPS compliance as SM2 is not a FIPS algorithm. Fixed versions are available.

Impact

An attacker able to measure the timing of SM2 signature generation can gain partial information about the secret nonce used in each signature. Accumulating timing data over many signatures may enable recovery of the private key through cryptanalytic methods. This compromises the confidentiality of the private key, potentially allowing signature forgery or impersonation. The impact is limited by the attack complexity and the requirement for precise timing measurements.

Summary

The vulnerability arises because OpenSSL's SM2 signature generation performs non-constant-time BIGNUM operations on secret nonce and private key values. This timing discrepancy forms a side-channel that can leak information about the per-signature secret nonce. An attacker capable of precisely measuring signature generation times can exploit this to recover the private key through advanced cryptanalysis techniques such as lattice or Hidden Number Problem attacks. The issue affects multiple OpenSSL versions prior to fixed releases. The CVSS 3.1 score is 3.7 (low severity), reflecting the network attack vector with high attack complexity and no privileges or user interaction required. No known exploits are reported in the wild.

CWE-208Observable Timing Discrepancy (opens in a new tab)
Base weakness
Two separate operations in a product require different amounts of time to complete, in a way that is observable to an actor and reveals security-relevant information about the state of the product, such as whether a particular operation was successful or not.
OWASP Cheat Sheets
Error Handling (opens in a new tab)
Logging (opens in a new tab)
OWASP ASVS 4.0.3
V8.3.4 (opens in a new tab)
V14.3.3 (opens in a new tab)
V7.3.3 (opens in a new tab)
Attack patterns
Cross-Domain Search Timing (opens in a new tab)
Application Fingerprinting (opens in a new tab)
System Footprinting (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 10 Nov 2026, 13:17 UTC

WeaknessesCWE-208

Technical details

References

Community reviews

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