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fix: verify MCP history reads #145

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fix: verify MCP history reads #145

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1 change: 1 addition & 0 deletions CHANGELOG.md
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Original file line number Diff line number Diff line change
Expand Up @@ -12,6 +12,7 @@

### Fixed

- Read MCP saved-history files through verified descriptors so path swaps cannot expose symbolic-link targets.
- Protect legacy and source-backed user/server memory reads and writes from symbolic links, junctions, and path swaps.
- Require a text response for `!ask` commands even when their prompt is phrased without a question mark.
- Remove malformed `[REACT:]` directives from legacy Claude responses instead of sending them as Discord text.
Expand Down
122 changes: 74 additions & 48 deletions src/mcp/server.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,7 @@ import {
MCP_FETCH_MESSAGES_MAX_LINKS,
MCP_READ_MESSAGES_MAX_CHARS,
MCP_HISTORY_MAX_CHARS,
MESSAGES_DIR,
PENDING_DIR,
} from "../config.js";
import { client } from "../discord/client.js";
Expand All @@ -28,6 +29,7 @@ import {
isCalendarDate,
} from "./historyFiles.js";
import { parseChannelHistoryFileName } from "../storage/historyPaths.js";
import { readVerifiedUtf8File } from "../storage/safeRead.js";

const ReactToMessageSchema = z.object({
server: z
Expand Down Expand Up @@ -55,12 +57,12 @@ function isWithinDiscordMessageLimit(message: string): boolean {
return true;
}

function readPendingMetadata(filePath: string): {
function readPendingMetadata(text: string): {
channelId: string | undefined;
channelName: string | undefined;
date: string | undefined;
} {
const lines = fs.readFileSync(filePath, "utf-8").split("\n");
const lines = text.split("\n");
const separatorIndex = lines.indexOf("---");
const headerLines = lines.slice(0, separatorIndex === -1 ? 4 : separatorIndex);
const channelLine = headerLines.find((line) => line.startsWith("Channel: #"));
Expand All @@ -86,6 +88,26 @@ function readPendingMetadata(filePath: string): {
};
}

interface ReadableHistoryFile {
displayName: string;
channelId: string | undefined;
channelName: string | undefined;
date: string | undefined;
text: string;
}

function readStoredHistoryFile(
filePath: string,
expectedDirectory: string,
): string | undefined {
const result = readVerifiedUtf8File(
filePath,
MESSAGES_DIR,
expectedDirectory,
);
return result.state === "valid" ? result.text : undefined;
}

const HISTORY_RESPONSE_SEPARATOR = "\n\n===\n\n";

function takeUtf16Suffix(text: string, maxChars: number): string {
Expand Down Expand Up @@ -496,54 +518,59 @@ export function createMcpServer(): Server {
"_",
)
: undefined;
let files = fs
.readdirSync(dir, { withFileTypes: true })
.filter(
(entry) =>
entry.isFile() && entry.name.endsWith(".txt"),
)
.map((entry) => {
const filePath = path.join(dir, entry.name);
const pendingMetadata =
type === "pending"
? readPendingMetadata(filePath)
: undefined;
return {
displayName: entry.name,
filePath,
channelId: pendingMetadata?.channelId,
channelName:
type === "history"
? getLegacyHistoryChannel(entry.name)
: pendingMetadata?.channelName,
date: pendingMetadata?.date,
};
let files: ReadableHistoryFile[] = [];
for (const entry of fs.readdirSync(dir, {
withFileTypes: true,
})) {
if (!entry.isFile() || !entry.name.endsWith(".txt")) {
continue;
}
const filePath = path.join(dir, entry.name);
const text = readStoredHistoryFile(filePath, dir);
if (text === undefined) continue;
const pendingMetadata = type === "pending"
? readPendingMetadata(text)
: undefined;
files.push({
displayName: entry.name,
channelId: pendingMetadata?.channelId,
channelName:
type === "history"
? getLegacyHistoryChannel(entry.name)
: pendingMetadata?.channelName,
date: pendingMetadata?.date,
text,
});
}

if (type === "history") {
const channelFiles = fs
.readdirSync(HISTORY_V2_DIR, { withFileTypes: true })
.filter(
(entry) =>
entry.isFile() &&
entry.name.endsWith(".txt"),
)
.map((entry) => {
const parsed = parseChannelHistoryFileName(
entry.name,
);
return {
displayName: `v2/${entry.name}`,
filePath: path.join(
HISTORY_V2_DIR,
entry.name,
),
channelId: parsed?.channelId,
channelName: parsed?.channelName,
date: undefined,
};
for (const entry of fs.readdirSync(HISTORY_V2_DIR, {
withFileTypes: true,
})) {
if (
!entry.isFile()
|| !entry.name.endsWith(".txt")
) continue;
const filePath = path.join(
HISTORY_V2_DIR,
entry.name,
);
const text = readStoredHistoryFile(
filePath,
HISTORY_V2_DIR,
);
if (text === undefined) continue;
const parsed = parseChannelHistoryFileName(
entry.name,
);
files.push({
displayName: `v2/${entry.name}`,
channelId: parsed?.channelId,
channelName: parsed?.channelName,
date: undefined,
text,
});
files.push(...channelFiles);
}
files.sort((left, right) =>
compareHistoryFilenames(
left.displayName,
Expand Down Expand Up @@ -577,8 +604,7 @@ export function createMcpServer(): Server {
: files.slice(-limit);
let matchingFiles = candidateFiles
.map((file) => {
let lines = fs
.readFileSync(file.filePath, "utf-8")
let lines = file.text
.split("\n")
.filter((line) => line.trim().length > 0);

Expand Down
30 changes: 30 additions & 0 deletions tests/mcpHistory.test.mjs
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Original file line number Diff line number Diff line change
Expand Up @@ -61,6 +61,11 @@ test("MCP history filters matching regular files and preserves pending indentati
path.join(historyDir, "linked_2026-08-01.txt"),
);
fs.mkdirSync(path.join(historyDir, "directory_2026-08-01.txt"));
const swappedHistoryFile = path.join(
historyDir,
"swapped_2026-08-01.txt",
);
fs.writeFileSync(swappedHistoryFile, "ordinary history entry\n", "utf8");
fs.symlinkSync(
outsideFile,
path.join(
Expand Down Expand Up @@ -124,6 +129,31 @@ test("MCP history filters matching regular files and preserves pending indentati
assert.doesNotMatch(text, /directory_2026-08-01\.txt/);
assert.doesNotMatch(text, /symlinked secret/);

const originalReaddirSync = fs.readdirSync;
fs.readdirSync = function patchedReaddirSync(directory, options) {
const entries = originalReaddirSync.call(fs, directory, options);
if (path.resolve(directory.toString()) === path.resolve(historyDir)) {
fs.rmSync(swappedHistoryFile, { force: true });
fs.symlinkSync(outsideFile, swappedHistoryFile);
}
return entries;
};
let swappedResult;
try {
swappedResult = await client.callTool({
name: "read-message-history",
arguments: { date: "2026-08-01" },
});
} finally {
fs.readdirSync = originalReaddirSync;
}
const swappedText = swappedResult.content.find(
(item) => item.type === "text",
)?.text;
assert.equal(typeof swappedText, "string");
assert.doesNotMatch(swappedText, /swapped_2026-08-01\.txt/);
assert.doesNotMatch(swappedText, /symlinked secret/);

const pendingResult = await client.callTool({
name: "read-message-history",
arguments: { type: "pending" },
Expand Down