fallow-core 2.86.0

//! Local security candidate detection (opt-in, surfaced only by `fallow security`).
//!
//! These are CANDIDATES for downstream agent verification, NOT verified
//! vulnerabilities. The MVP ships one graph-structural rule, `client-server-leak`:
//! a `"use client"` file that transitively imports a module reading a non-public
//! `process.env` secret. fallow emits the structural import-hop trace; it does not
//! prove the path is exploitable.
//!
//! Blind spots (surfaced in-band via [`UnresolvedEdgeStats`], not silently
//! dropped): the BFS follows only resolved static import edges, so dynamic
//! `import()` and unresolved specifiers can hide a real leak. `import.meta.env`
//! reads (the Vite secret convention) are not modeled as secret sources.

use rustc_hash::{FxHashMap, FxHashSet};
use std::collections::VecDeque;

use fallow_types::extract::ModuleInfo;
use fallow_types::output::{IssueAction, SuppressFileAction, SuppressFileKind};
use fallow_types::results::{SecurityFinding, SecurityFindingKind, TraceHop, TraceHopRole};
use fallow_types::suppress::IssueKind;

use super::{LineOffsetsMap, byte_offset_to_line_col};
use crate::discover::FileId;
use crate::graph::ModuleGraph;
use crate::suppress::SuppressionContext;

mod catalogue;
mod tainted_sink;

pub use catalogue::catalogue_title;
pub use tainted_sink::{CategoryFilter, find_tainted_sinks};

/// The inline suppression kind token for the client-server-leak rule.
const SUPPRESS_KIND: &str = "security-client-server-leak";

/// Build the machine-actionable suppress hint emitted on every finding. Single
/// file-level suppress action (`auto_fixable: false`): there is no auto-fix
/// because verifying the candidate is the agent's job, not fallow's.
fn build_actions() -> Vec<IssueAction> {
    vec![IssueAction::SuppressFile(SuppressFileAction {
        kind: SuppressFileKind::SuppressFile,
        auto_fixable: false,
        description: "Suppress with a file-level comment at the top of the client file".to_string(),
        comment: format!("// fallow-ignore-file {SUPPRESS_KIND}"),
    })]
}

/// The React Server Components client-boundary directive.
const USE_CLIENT: &str = "use client";

/// Singular/plural noun for the count of secret vars named in the evidence.
const fn secret_word(count: usize) -> &'static str {
    if count == 1 { "secret" } else { "secrets" }
}

/// `process.env` var-name prefixes that frameworks inline into the client bundle
/// by convention. A read of one of these from a client file is normal and safe,
/// so it does NOT mark a module as a secret source.
const PUBLIC_ENV_PREFIXES: &[&str] = &[
    "NEXT_PUBLIC_",
    "VITE_",
    "NUXT_PUBLIC_",
    "REACT_APP_",
    "PUBLIC_",
    "GATSBY_",
    "EXPO_PUBLIC_",
    "STORYBOOK_",
];

/// Exact `process.env` var names that are public by convention (no prefix).
const PUBLIC_ENV_EXACT: &[&str] = &["NODE_ENV"];

/// The `member_accesses` object string for a `process.env.X` read.
const PROCESS_ENV_OBJECT: &str = "process.env";

/// Whether a `process.env` var name is public-by-convention (build-inlined into
/// the client bundle), and therefore not a secret.
fn is_public_env_var(name: &str) -> bool {
    PUBLIC_ENV_EXACT.contains(&name) || PUBLIC_ENV_PREFIXES.iter().any(|p| name.starts_with(p))
}

/// Blind-spot accounting surfaced in-band so the user is never told "clean" when
/// the analysis could not see part of the import graph.
#[derive(Debug, Default, Clone, Copy)]
pub struct UnresolvedEdgeStats {
    /// Number of `"use client"` files whose transitive import cone contains a
    /// dynamic `import()` pattern the reachability BFS cannot follow, so a leak
    /// could be hiding behind it.
    pub client_files_with_unresolved_edges: usize,
}

/// Run the security MVP rules over the graph. Returns the findings plus the
/// blind-spot stats. Callers gate this on the `security_client_server_leak`
/// rule severity; it never runs under bare `fallow` or the `audit` gate.
#[must_use]
pub fn find_security_findings(
    graph: &ModuleGraph,
    modules: &[ModuleInfo],
    suppressions: &SuppressionContext<'_>,
    line_offsets_by_file: &LineOffsetsMap<'_>,
) -> (Vec<SecurityFinding>, UnresolvedEdgeStats) {
    let modules_by_id: FxHashMap<FileId, &ModuleInfo> =
        modules.iter().map(|m| (m.file_id, m)).collect();

    let secret_sources = compute_secret_source_set(&modules_by_id);

    find_client_server_leaks(
        graph,
        &modules_by_id,
        &secret_sources,
        suppressions,
        line_offsets_by_file,
    )
}

/// Map each module that reads a non-public `process.env` secret to the var names
/// it reads. `process.env.X` reads surface as `MemberAccess { object:
/// "process.env", member: "X" }` (a side effect of static-member capture), so no
/// new extraction is needed. `import.meta.env` is not captured (documented gap).
fn compute_secret_source_set(
    modules_by_id: &FxHashMap<FileId, &ModuleInfo>,
) -> FxHashMap<FileId, Vec<String>> {
    let mut sources: FxHashMap<FileId, Vec<String>> = FxHashMap::default();
    for (&file_id, module) in modules_by_id {
        let mut vars: Vec<String> = module
            .member_accesses
            .iter()
            .filter(|ma| ma.object == PROCESS_ENV_OBJECT && !is_public_env_var(&ma.member))
            .map(|ma| ma.member.clone())
            .collect();
        if vars.is_empty() {
            continue;
        }
        vars.sort_unstable();
        vars.dedup();
        sources.insert(file_id, vars);
    }
    sources
}

/// For each `"use client"` file, BFS its transitive static-import cone; if it
/// reaches a secret source, emit one finding anchored on the client file with
/// the shortest-path trace. Type-only edges are skipped (erased at build, so
/// they cannot carry a secret into the client bundle).
fn find_client_server_leaks(
    graph: &ModuleGraph,
    modules_by_id: &FxHashMap<FileId, &ModuleInfo>,
    secret_sources: &FxHashMap<FileId, Vec<String>>,
    suppressions: &SuppressionContext<'_>,
    line_offsets_by_file: &LineOffsetsMap<'_>,
) -> (Vec<SecurityFinding>, UnresolvedEdgeStats) {
    let mut findings = Vec::new();
    let mut stats = UnresolvedEdgeStats::default();

    for node in &graph.modules {
        let Some(module) = modules_by_id.get(&node.file_id) else {
            continue;
        };
        if !module.directives.iter().any(|d| d == USE_CLIENT) {
            continue;
        }
        let client_id = node.file_id;
        // A file-level `// fallow-ignore-file security-client-server-leak`
        // (or a blanket file ignore) opts the whole client file out. Routed
        // through the SuppressionContext so the marker is recorded as consumed
        // (otherwise a working suppression would later be flagged stale).
        if suppressions.is_file_suppressed(client_id, IssueKind::SecurityClientServerLeak) {
            continue;
        }

        // Direct case: the client file itself reads a non-public secret. The
        // most direct leak; no import hop needed.
        if secret_sources.contains_key(&client_id) {
            findings.push(build_direct_finding(graph, client_id, secret_sources));
            // Still count its dynamic-import blind spot below.
        }

        // Transitive case: BFS the import cone. parent maps child ->
        // (parent, span_start of the parent's import).
        let mut visited: FxHashSet<FileId> = FxHashSet::default();
        visited.insert(client_id);
        let mut parent: FxHashMap<FileId, (FileId, Option<u32>)> = FxHashMap::default();
        let mut queue: VecDeque<FileId> = VecDeque::new();
        queue.push_back(client_id);
        let mut had_unresolved_edge = false;
        let mut reached_secret: Option<FileId> = None;

        // Drain the FULL cone (no early break): the first secret reached via BFS
        // is the shortest-path trace, but we keep going so the dynamic-import
        // blind-spot count reflects the whole cone, not just the path to the
        // first secret (otherwise a leak hidden behind a dynamic edge past the
        // first finding would be silently uncounted).
        while let Some(current) = queue.pop_front() {
            if let Some(current_module) = modules_by_id.get(&current)
                && !current_module.dynamic_import_patterns.is_empty()
            {
                had_unresolved_edge = true;
            }

            if current != client_id
                && reached_secret.is_none()
                && secret_sources.contains_key(&current)
            {
                reached_secret = Some(current);
            }

            for (target, all_type_only, span_start) in graph.outgoing_edge_summaries(current) {
                if all_type_only {
                    continue; // type-only imports are erased at build; cannot leak.
                }
                if visited.insert(target) {
                    parent.insert(target, (current, span_start));
                    queue.push_back(target);
                }
            }
        }

        if had_unresolved_edge {
            stats.client_files_with_unresolved_edges += 1;
        }

        // Only emit a transitive finding when the client is not ALREADY flagged
        // by the direct case (avoid double-flagging the same file).
        if let Some(secret_id) = reached_secret
            && !secret_sources.contains_key(&client_id)
        {
            findings.push(build_leak_finding(
                graph,
                client_id,
                secret_id,
                &parent,
                secret_sources,
                line_offsets_by_file,
            ));
        }
    }

    findings.sort_by(|a, b| a.path.cmp(&b.path).then(a.line.cmp(&b.line)));
    (findings, stats)
}

/// Reconstruct the shortest path `client -> ... -> secret` from the BFS parent
/// map and build the finding. Each non-terminal hop's line is the import site in
/// that file (where it imports the next hop); the secret-source hop has no
/// outgoing edge in the chain so it anchors at line 1.
fn build_leak_finding(
    graph: &ModuleGraph,
    client_id: FileId,
    secret_id: FileId,
    parent: &FxHashMap<FileId, (FileId, Option<u32>)>,
    secret_sources: &FxHashMap<FileId, Vec<String>>,
    line_offsets_by_file: &LineOffsetsMap<'_>,
) -> SecurityFinding {
    // Walk parent pointers from the secret back to the client, then reverse.
    let mut chain: Vec<FileId> = vec![secret_id];
    let mut cursor = secret_id;
    while let Some(&(prev, _)) = parent.get(&cursor) {
        chain.push(prev);
        cursor = prev;
        if prev == client_id {
            break;
        }
    }
    chain.reverse(); // now [client_id, ..., secret_id]

    let mut trace: Vec<TraceHop> = Vec::with_capacity(chain.len());
    for (idx, &file_id) in chain.iter().enumerate() {
        let role = if idx == 0 {
            TraceHopRole::ClientBoundary
        } else if file_id == secret_id {
            TraceHopRole::SecretSource
        } else {
            TraceHopRole::Intermediate
        };
        // The line for a non-terminal hop is where it imports the NEXT hop.
        // Member-access extraction does not yet carry spans, so the terminal
        // secret-source hop falls back to the source module start.
        let (line, col) = if let Some(&next) = chain.get(idx + 1) {
            parent
                .get(&next)
                .and_then(|&(_, span)| span)
                .map_or((1, 0), |s| {
                    byte_offset_to_line_col(line_offsets_by_file, file_id, s)
                })
        } else {
            (1, 0)
        };
        trace.push(TraceHop {
            path: graph.modules[file_id.0 as usize].path.clone(),
            line,
            col,
            role,
        });
    }

    let anchor = &trace[0];
    let empty = Vec::new();
    let var_list = secret_sources.get(&secret_id).unwrap_or(&empty);
    let vars = var_list.join(", ");
    let word = secret_word(var_list.len());
    // Do NOT embed the secret file path in the message: the SecretSource trace
    // hop already names it (and is root-relativized by the CLI before display),
    // so embedding the absolute path here would leak it past relativization and
    // make output environment-dependent.
    let evidence = format!(
        "This \"use client\" file transitively imports a module that reads non-public \
         process.env {word}: {vars} (see the secret-source hop in the trace). Candidate for \
         verification: confirm the secret value actually reaches client-bundled code."
    );

    SecurityFinding {
        kind: SecurityFindingKind::ClientServerLeak,
        category: None,
        cwe: None,
        path: anchor.path.clone(),
        line: anchor.line,
        col: anchor.col,
        evidence,
        trace,
        actions: build_actions(),
    }
}

/// Build a finding for the direct case: a `"use client"` file that itself reads
/// a non-public secret. Trace is a single hop on the client file, which is both
/// the boundary and the secret source.
fn build_direct_finding(
    graph: &ModuleGraph,
    client_id: FileId,
    secret_sources: &FxHashMap<FileId, Vec<String>>,
) -> SecurityFinding {
    let path = graph.modules[client_id.0 as usize].path.clone();
    let empty = Vec::new();
    let var_list = secret_sources.get(&client_id).unwrap_or(&empty);
    let vars = var_list.join(", ");
    let word = secret_word(var_list.len());
    let evidence = format!(
        "This \"use client\" file directly reads non-public process.env {word}: {vars}. \
         Candidate for verification: confirm the secret value actually reaches client-bundled \
         code (it may be guarded, server-only, or build-time-stripped)."
    );
    SecurityFinding {
        kind: SecurityFindingKind::ClientServerLeak,
        category: None,
        cwe: None,
        path: path.clone(),
        line: 1,
        col: 0,
        evidence,
        trace: vec![TraceHop {
            path,
            line: 1,
            col: 0,
            role: TraceHopRole::SecretSource,
        }],
        actions: build_actions(),
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn public_env_vars_are_not_secrets() {
        assert!(is_public_env_var("NODE_ENV"));
        assert!(is_public_env_var("NEXT_PUBLIC_API_URL"));
        assert!(is_public_env_var("VITE_TITLE"));
        assert!(is_public_env_var("PUBLIC_SITE_NAME"));
        assert!(is_public_env_var("EXPO_PUBLIC_KEY"));
    }

    #[test]
    fn real_secrets_are_not_public() {
        assert!(!is_public_env_var("DATABASE_URL"));
        assert!(!is_public_env_var("STRIPE_SECRET_KEY"));
        assert!(!is_public_env_var("SESSION_SECRET"));
        // A var that merely contains a public token mid-name is still a secret.
        assert!(!is_public_env_var("MY_NEXT_PUBLIC_FAKE"));
    }
}