Security & cryptography

Parameterization protects query structure. It does not add an ownership predicate or establish tenant membership.

The user can request another organization's object if the server checks only identity. Load authority from the authenticated server-side principal and current membership or policy data, and constrain the lookup to objects that principal may read. A query can join documents to authorized memberships or a policy layer can evaluate the retrieved resource before returning any sensitive fields. Browser-supplied organization IDs are selectors, not proof of authority. Deny by default and apply the same rule to exports, attachments, search snippets, and alternate endpoints.

Define whether revoked membership takes effect immediately or after a documented cache/session interval; invalidate or recheck cached authority accordingly. Decide whether unauthorized and absent objects share a response to reduce existence leakage, while retaining useful internal audit records. Test cross-tenant IDs, revoked users, read-only roles attempting writes, missing objects, and direct API calls that bypass the UI. Parameterized SQL remains necessary for injection resistance but solves a different problem.

Check your reasoning

• Separate identity, query safety, and object authorization.
• Derive authority from trusted server state.
• Test alternate data paths and revocation.

An unkeyed digest is computable by the attacker. For a reused keystream K, C1 XOR C2 cancels K.

The attacker can replace the ciphertext and recompute its public digest, so the hash detects accidental corruption but not malicious replacement. With C1=P1 XOR K and C2=P2 XOR K, their XOR is P1 XOR P2; known structure or known plaintext can expose information about the other message. Authenticated encryption combines confidentiality with integrity under its precise nonce and key requirements. Use a reviewed library, generate or allocate nonces according to the selected scheme, and never assume all AEAD algorithms tolerate reuse.

Bind tenant ID, record ID, format version, and other context as associated data when those fields must be authenticated without being encrypted. Store a key identifier, keep keys outside the data store with access controls, and define rotation, backup recovery, and compromised-key response. Verify authentication before using plaintext, and avoid revealing detailed decryption failures externally. Password verification should use a dedicated salted, deliberately expensive password-hashing scheme with reviewed parameters; reversible encryption is inappropriate when the service only needs to verify a password. Neither encryption nor hashing repairs excessive access permissions or sensitive logging.

Check your reasoning

• Show why an attacker can recompute the digest.
• Derive the keystream-cancellation equation.
• State nonce, context-binding, and key-lifecycle requirements.

Cookies can be ambient credentials. CORS primarily controls a script's access to responses; some cross-origin requests can still be sent.

A malicious site can cause a victim's browser to submit a request while the browser attaches eligible cookies. The server sees a valid session but lacks evidence that the user intended this action. Use an appropriate CSRF token or a well-designed custom-header pattern, validate Origin or suitable request metadata, and set cookies with Secure, HttpOnly, and an appropriate SameSite policy. Require authorization and validate the operation independently. Sensitive actions may need explicit recent user verification.

POST alone does not prevent cross-site form submission. Strict JSON handling and custom headers can block simple cross-origin forms when correctly enforced, but accepting alternate content types, permissive origins, or unsafe endpoints can invalidate that design. CORS is not a universal CSRF defense, because blocking response reads does not necessarily block the effect. SameSite reduces attack surface but depends on site boundaries, navigation behavior, and application flows. Same-origin script injection can often read tokens or issue authorized requests, so CSRF controls do not replace output encoding, safe DOM APIs, and defenses against script injection. Test the actual browser and endpoint behavior, including rejected content types and missing or mismatched tokens.

Check your reasoning

• Explain ambient-cookie authority.
• Use a defined anti-CSRF design with defense in depth.
• Separate CSRF, CORS, and same-origin script execution.

Exposure removal does not invalidate copies. Find the transitive authority of the credential, not only its displayed permissions.

Contain by revoking or disabling the exposed credential and restricting affected access while maintaining essential service through a controlled replacement. Preserve relevant logs and timestamps in an access-controlled location before destructive cleanup, and record when exposure and revocation occurred. Determine which objects and operations the credential could reach, whether it could create credentials or change policy, and whether those derived capabilities also require revocation. Public-log deletion limits further exposure but cannot recall copies already obtained.

Assess access logs, configuration changes, downloads, and suspicious activity across the exposure window, while acknowledging logging gaps and retention limits. Rotate dependent secrets only where their exposure or derivation is plausible, restore trusted configuration, and verify that the old credential and any descendants fail while the replacement has only required permissions. Test application recovery, not merely credential creation. Prevent recurrence through short-lived scoped credentials, secret redaction and scanning, least privilege, safer build outputs, and a rehearsed response path. Communicate facts and uncertainty through the organization's incident process; absence of a log entry is not proof that no access occurred.

Check your reasoning

• Revoke usable authority, including derived credentials.
• Preserve evidence and identify its limits.
• Verify both denied old access and functioning least-privilege replacement.