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Venmo’s 2019 API case is a reminder that exposure does not always require a software exploit: data can be accessible because a service or its settings make it public. The practical lessons are to govern third-party access, limit permissions, secure APIs throughout their lifecycle, protect sensitive data, and monitor how APIs are used. The historical figures below describe activity reported in 2019, not Venmo’s current service.
What happened in the Venmo API case?
In a feature published July 30, 2019, CSO’s Maria Korolov reported that researchers accessed large numbers of Venmo transactions through an API. The article characterized the issue as public access to transaction data, not a conventional exploit that bypassed authorization. That distinction matters: an API can return information as designed and still create serious privacy risks if the information is too broadly visible.
CSO reported that a computer science student accessed seven million Venmo transactions in 2019 and that another researcher had downloaded more than 200 million transactions the previous year. These are historical figures reported in 2019, not current measurements of Venmo activity or evidence that the same endpoint or conditions remain in place.
Payment descriptions can disclose more than the mechanics of a transaction. As CSO noted, descriptions may reveal sensitive context, and a collection of seemingly ordinary details can help someone build a picture of a person’s relationships or routine. That information can also support social engineering.
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Six security lessons from the case
1. Govern partner access, not just your own API
When a third-party service or integration receives data, the organization needs to know what it can access, why it needs that access, and how it handles the data afterward. Restrict access to the minimum necessary, set expectations for retention and onward sharing, and review those arrangements over time. Data copied outside your control may be difficult to retrieve even if you later change a setting or revoke access.
2. Secure the full API surface
API security is not a single authentication setting. Review who can connect, which resources each client can reach, and whether implementation flaws expose data or actions beyond the intended scope. Test related services and infrastructure as well as the endpoint itself: an API’s risk may come from a weakness elsewhere in the product, not from the API’s public behavior.
Keep the categories clear. A publicly accessible feed is a disclosure and governance problem; a bug that lets a client access data it should not see is an authorization or implementation failure. Both can be serious, but they call for different fixes.
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3. Treat accidental exposure and permissions as ongoing risks
Users and administrators often grant integrations more access than a task requires, or forget that an old connection remains active. Make permissions narrow by default, explain what a grant allows, and provide a way to review and revoke it. Organizations should periodically inventory integrations and remove those no longer needed.
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An incident described as an “API breach” may begin with exposed infrastructure, a compromised product, or a weakness in a connected component rather than the API implementation. Incident response should trace how the data became reachable and which systems, credentials, and integrations were involved before choosing a remedy.
5. Match encryption and authentication to the data and access need
Encrypt data in transit and authenticate clients, but do not treat either measure as proof that a request is allowed. Authentication answers who or what is connecting; authorization determines what that identity may access. A valid client can still have excessive permissions, and encrypted traffic can still carry data to the wrong recipient.
CSO’s 2019 article included advice about basic authentication and certificates. Those quotations reflect recommendations reported at that time, not a current implementation standard. For contemporary design, NIST’s Special Publication 800-228, updated March 13, 2026, recommends selecting API controls according to risk across development and runtime rather than relying on one control for every API.
6. Monitor API use and have a response plan
Preventive controls cannot reliably identify every misuse or compromised credential. Record enough activity to see who accessed which resources and when, then look for unusual volume, unexpected access patterns, or behavior inconsistent with a client’s normal purpose. Monitoring only helps if someone owns the alerts and can investigate, limit access, and respond to confirmed abuse.
How to apply the lessons across an API lifecycle
NIST SP 800-228 frames API security as a lifecycle problem: analyze risk during development and runtime, apply appropriate controls before runtime and at runtime, and adopt improvements incrementally. A practical review can follow this sequence:
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- Inventory the APIs and data. Identify public and internal interfaces, the information or actions they expose, and connected services. Classify data by sensitivity and consider what can be inferred when records are combined.
- Define identities and permissions. Specify which users, services, and integrations may call each API and the minimum scope each needs. Separate authentication from authorization in both design and testing.
- Assess controls before release. Review implementation and configuration for unintended access, excessive permissions, and weaknesses in supporting systems. Test the controls against the API’s risk and data sensitivity.
- Operate with visibility. Monitor access and investigate anomalous activity. Establish who responds, how access can be limited, and how affected integrations or credentials can be disabled.
- Reassess when conditions change. Revisit permissions, partner access, and risk when APIs, integrations, data uses, or operating conditions change. Remove access that no longer has a defined purpose.
What the FTC matter does—and does not—show
The Federal Trade Commission’s February 2018 announcement concerned a separate matter. The FTC alleged that Venmo inadequately disclosed transfer limitations and privacy settings, misrepresented account security, and failed to send notifications for certain account changes; the announcement described settlement requirements and related prohibitions. Those allegations and requirements are not proof that the later-reported public API access was a software exploit, nor do they establish present-day conduct. See the FTC’s February 2018 announcement for the agency’s account.
What Venmo’s current guidance says about privacy and security
Venmo’s privacy statement, effective November 17, 2025, says that public profile information includes a username, profile photo, first and last name, account creation month and year, and public transactions. It says public information can be seen by anyone online and may be accessed, reshared, or downloaded through Venmo APIs and integrated third-party services. Friends-list visibility is available to logged-in users and can be adjusted in settings. This does not mean all Venmo transactions are public; visibility depends on what is designated public and the relevant settings. Read the Venmo Privacy Statement for its current terms.
Venmo’s security guidance describes encryption, activity monitoring, multifactor authentication, and PIN use. It also explains removing a lost phone’s session and warns that payments to strangers can be high risk and may lack buyer or seller protection. These user-facing controls help protect accounts, but they do not replace sound API authorization, data-sharing governance, or monitoring by the service provider.
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What the historical numbers can tell us
CSO’s 2019 feature also reported broader industry figures, which should be read as historical reports rather than current benchmarks. It attributed to a Ping Identity survey that 60% of surveyed companies had more than 400 APIs, 51% were unsure security teams knew about every API, and 45% lacked confidence in detecting bad-actor access. The feature also attributed to Akamai a finding that 30% of API authentication attempts were fraudulent. Those original survey and report materials are not cited here, so the figures are best understood as numbers CSO reported in 2019, not independently verified or representative of conditions today.
The same article quoted Okta’s Keith Casey describing Venmo’s APIs as “an unlocked front door to a treasure trove of insights,” referring to the 40 million active users cited in that 2019 coverage. Neither that user count nor the quoted assessment should be treated as a current measurement.
How should users think about API-related privacy?
For an individual user, the immediate question is what information is public and which integrations can access the account. Review privacy settings and connected apps in the service, grant only access you understand, and revoke integrations you no longer use. Venmo recommends multifactor authentication and an in-app PIN; its guidance also explains how to remove a lost phone’s session. These steps can reduce account risk, but they cannot make information private after it has been made public or copied by another service.
For an organization building an API, the parallel is to make disclosure intentional: publish only what the use case requires, explain visibility clearly, scope access narrowly, and operate controls that detect and respond to misuse. NIST’s current API framework is a useful reference for choosing those controls according to risk.
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