VulnerabilityPublished 21 Jan 2026

CVE-2026-23996: Athroniaeth fastapi-api-key · Timing Side Channel

Affects Athroniaeth fastapi-api-keySource CVE Database V5

Not known to be exploited · CVSS 3.7 Low : upgrade to 1.1.0 when convenient.

Data as of 26 Oct 2026, 14:05 UTC

CVSS 3.1 base score

3.7Low

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

EPSS: 0.2% chance of exploitation in 30 days – higher than 21% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 1.1.0

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 21 Jan 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: 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 26 Oct 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.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, 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 Athroniaeth fastapi-api-key to 1.1.0.

Affected software

Product	Affected	Fixed in
Athroniaethfastapi-api-key	Affected <1.1.0	Fixed in 1.1.0
PyPIfastapi-api-key`pkg:pypi/fastapi-api-key`Other threats	Affected <1.1.0	Fixed in 1.1.0

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

The primary mitigation is to upgrade fastapi-api-key to version 1.1.0 or later, which includes a patch applying uniform random delays to all verification responses, eliminating timing discrepancies. Until upgrading is feasible, organizations should implement application-level mitigations such as adding fixed or randomized delays (jitter) uniformly to all API key verification responses, regardless of success or failure, to mask timing differences. Additionally, deploying strict rate limiting and throttling on API endpoints can reduce the feasibility of repeated timing measurements by attackers. Monitoring and logging authentication attempts for unusual patterns can help detect brute-force or enumeration activities early. Organizations should also review API key management policies to ensure keys are rotated regularly and follow the principle of least privilege. Finally, educating developers about timing side-channel risks and secure coding practices can prevent similar vulnerabilities in the future.

Description

CVE-2026-23996 is a timing side-channel vulnerability in the fastapi-api-key library version prior to 1.1.0. The verify_key() function applies a random delay only on verification failures, enabling attackers to statistically distinguish valid API keys by measuring response times. This can facilitate brute-force or enumeration attacks against API keys. The vulnerability impacts confidentiality by revealing valid key existence but does not affect integrity or availability. The issue is fixed in version 1.1.0 by applying uniform random delays to all responses. Mitigations include upgrading to 1.

Impact

For European organizations, this vulnerability primarily threatens the confidentiality of API key information by enabling attackers to identify valid keys through timing analysis. This can lead to accelerated brute-force or enumeration attacks, potentially exposing sensitive APIs to unauthorized access. While the vulnerability does not directly compromise data integrity or availability, the exposure of valid API keys can facilitate further attacks or unauthorized data access. Organizations relying on fastapi-api-key for API authentication, especially those with public-facing APIs or critical backend services, face increased risk if unpatched. The impact is more pronounced in sectors with high API usage such as fintech, e-commerce, and cloud services. Additionally, the vulnerability could undermine trust in API security and compliance with data protection regulations like GDPR if unauthorized access occurs. However, the low CVSS score and absence of known exploits suggest the immediate risk is limited but should not be ignored.

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

Community reviews

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 29 Jan 2026, 08:49 UTC

WeaknessesCWE-208

Technical details

References

Community reviews

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