diff --git a/apps/api/src/routes/contest.ts b/apps/api/src/routes/contest.ts
index 9840e60..9b24edf 100644
--- a/apps/api/src/routes/contest.ts
+++ b/apps/api/src/routes/contest.ts
@@ -8,10 +8,10 @@ import {
   problemDetailSchema,
   problemListItemSchema,
 } from "@oj2/contract"
-import { and, asc, count, desc, eq, gte, ilike, inArray, isNull, lte, sql } from "drizzle-orm"
+import { and, asc, count, desc, eq, gte, ilike, inArray, lte, sql } from "drizzle-orm"
 import { Hono } from "hono"
 
-import { optionalAuth, requireAuth, type AppEnv } from "../auth/middleware"
+import { optionalAuth, requireAuth } from "../auth/middleware"
 import { setContestPassword } from "../auth/session"
 import { db, schema } from "../db"
 import { failure, success } from "../http"
@@ -22,10 +22,12 @@ import {
   contestStatus,
   findVisibleContest,
   isContestAdmin,
+  requireContestAccess,
+  type ContestEnv,
 } from "../services/contest"
 import { objectValue, publicTemplates, queryInteger, sampleUser, stringArray } from "./helpers"
 
-export const contestRoutes = new Hono<AppEnv>()
+export const contestRoutes = new Hono<ContestEnv>()
 
 async function creator(id: number) {
   const [row] = await db.select({ id: schema.user.id, username: schema.user.username, realName: schema.userProfile.realName })
@@ -110,11 +112,8 @@ async function contestProblemTags(problemIds: number[]) {
   return map
 }
 
-contestRoutes.get("/contests/:id/problems", optionalAuth, async (c) => {
-  const contest = await findVisibleContest(queryInteger(c.req.param("id"), 0, { min: 1 }))
-  if (!contest) return failure(c, 404, "contest-not-found", "Contest does not exist")
-  const access = await canAccessContest(c, contest, "problems")
-  if (!access.ok) return failure(c, access.code === "login-required" ? 401 : 403, access.code, access.message)
+contestRoutes.get("/contests/:id/problems", optionalAuth, requireContestAccess("problems"), async (c) => {
+  const contest = c.get("contest")!
   const rows = await db.select({ problem: schema.problem, user: schema.user, realName: schema.userProfile.realName })
     .from(schema.problem).innerJoin(schema.user, eq(schema.problem.createdById, schema.user.id))
     .leftJoin(schema.userProfile, eq(schema.userProfile.userId, schema.user.id))
@@ -138,11 +137,8 @@ contestRoutes.get("/contests/:id/problems", optionalAuth, async (c) => {
   })))
 })
 
-contestRoutes.get("/contests/:id/problems/:displayId", optionalAuth, async (c) => {
-  const contest = await findVisibleContest(queryInteger(c.req.param("id"), 0, { min: 1 }))
-  if (!contest) return failure(c, 404, "contest-not-found", "Contest does not exist")
-  const access = await canAccessContest(c, contest, "problems")
-  if (!access.ok) return failure(c, access.code === "login-required" ? 401 : 403, access.code, access.message)
+contestRoutes.get("/contests/:id/problems/:displayId", optionalAuth, requireContestAccess("problems"), async (c) => {
+  const contest = c.get("contest")!
   const [row] = await db.select({ problem: schema.problem, user: schema.user, realName: schema.userProfile.realName })
     .from(schema.problem).innerJoin(schema.user, eq(schema.problem.createdById, schema.user.id))
     .leftJoin(schema.userProfile, eq(schema.userProfile.userId, schema.user.id))
@@ -187,11 +183,8 @@ contestRoutes.get("/contests/:id/problems/:displayId", optionalAuth, async (c) =
   }))
 })
 
-contestRoutes.get("/contests/:id/rank", optionalAuth, async (c) => {
-  const contest = await findVisibleContest(queryInteger(c.req.param("id"), 0, { min: 1 }))
-  if (!contest) return failure(c, 404, "contest-not-found", "Contest does not exist")
-  const access = await canAccessContest(c, contest, "ranks")
-  if (!access.ok) return failure(c, access.code === "login-required" ? 401 : 403, access.code, access.message)
+contestRoutes.get("/contests/:id/rank", optionalAuth, requireContestAccess("ranks"), async (c) => {
+  const contest = c.get("contest")!
   const limit = queryInteger(c.req.query("limit"), 10, { min: 1, max: 250 })
   const offset = queryInteger(c.req.query("offset"), 0, { min: 0 })
   const where = and(eq(schema.acmContestRank.contestId, contest.id), inArray(schema.user.adminType, ["Regular User", "Student Admin"]), eq(schema.user.isDisabled, false))
diff --git a/apps/api/src/routes/submission.ts b/apps/api/src/routes/submission.ts
index 288c2ad..5242297 100644
--- a/apps/api/src/routes/submission.ts
+++ b/apps/api/src/routes/submission.ts
@@ -14,7 +14,7 @@ import {
 import { and, count, desc, eq, ilike, inArray, isNull, sql } from "drizzle-orm"
 import { Hono } from "hono"
 
-import { optionalAuth, requireAuth, type AppEnv } from "../auth/middleware"
+import { optionalAuth, requireAuth } from "../auth/middleware"
 import type { AuthUser } from "../auth/session"
 import { db, schema } from "../db"
 import { failure, success } from "../http"
@@ -26,6 +26,8 @@ import {
   findVisibleContest,
   ipAllowed,
   isContestAdmin,
+  requireContestAccess,
+  type ContestEnv,
 } from "../services/contest"
 import { CodeFormatError, formatCode } from "../services/format-code"
 import { getBooleanOption } from "../services/options"
@@ -40,7 +42,7 @@ import {
   todayStart,
 } from "./helpers"
 
-export const submissionRoutes = new Hono<AppEnv>()
+export const submissionRoutes = new Hono<ContestEnv>()
 
 function stringArray(value: unknown): string[] {
   return Array.isArray(value)
@@ -68,6 +70,8 @@ submissionRoutes.post("/submissions", requireAuth, async (c) => {
   }
   let contestId: number | null = null
   if (parsed.data.contestId) {
+    // 这里用不了 requireContestAccess 中间件：比赛 id 来自请求体，
+    // 中间件跑的时候 body 还没解析。全仓只有这一处仍是手工调用，改动时留意别漏掉鉴权。
     const contest = await findVisibleContest(parsed.data.contestId)
     if (!contest) return failure(c, 404, "contest-not-found", "Contest does not exist")
     const access = await canAccessContest(c, contest, "problems")
@@ -462,11 +466,8 @@ submissionRoutes.get("/submissions", optionalAuth, async (c) => {
   }))
 })
 
-submissionRoutes.get("/contests/:contestId/submissions", optionalAuth, async (c) => {
-  const contest = await findVisibleContest(queryInteger(c.req.param("contestId"), 0, { min: 1 }))
-  if (!contest) return failure(c, 404, "contest-not-found", "Contest does not exist")
-  const access = await canAccessContest(c, contest, "submissions")
-  if (!access.ok) return failure(c, access.code === "login-required" ? 401 : 403, access.code, access.message)
+submissionRoutes.get("/contests/:contestId/submissions", optionalAuth, requireContestAccess("submissions", "contestId"), async (c) => {
+  const contest = c.get("contest")!
   const limit = queryInteger(c.req.query("limit"), 10, { min: 1, max: 250 })
   const offset = queryInteger(c.req.query("offset"), 0, { min: 0 })
   const filters = [eq(schema.submission.contestId, contest.id)]
diff --git a/apps/api/src/services/contest.ts b/apps/api/src/services/contest.ts
index 47c9cc6..7595876 100644
--- a/apps/api/src/services/contest.ts
+++ b/apps/api/src/services/contest.ts
@@ -1,15 +1,27 @@
 import { createHash } from "node:crypto"
 
 import { and, eq } from "drizzle-orm"
-import type { Context } from "hono"
+import type { Context, MiddlewareHandler } from "hono"
 
 import type { AppEnv } from "../auth/middleware"
 import type { AuthUser } from "../auth/session"
 import { getContestPassword } from "../auth/session"
 import { db, schema } from "../db"
+import { failure } from "../http"
 
 export type ContestRow = typeof schema.contest.$inferSelect
 
+/**
+ * 走过 requireContestAccess 的路由，可以从 c.var.contest 直接拿到已鉴权的比赛。
+ *
+ * 类型上是可选的（同一个 router 里还有不涉及比赛的路由），所以 handler 里要写 `!`。
+ * 万一漏挂中间件，这里会在运行时抛错变成 500 —— 吵闹但安全，
+ * 而漏调 canAccessContest 是静默放行，两者不可同日而语。
+ */
+export interface ContestEnv extends AppEnv {
+  Variables: AppEnv["Variables"] & { contest?: ContestRow }
+}
+
 export function contestStatus(contest: ContestRow) {
   const now = Date.now()
   if (Date.parse(contest.startTime) > now) return "1" as const
@@ -42,8 +54,10 @@ export async function findVisibleContest(id: number) {
   return contest ?? null
 }
 
-export async function canAccessContest(
-  c: Context<AppEnv>,
+// 泛型而不是写死 Context<AppEnv>：requireContestAccess 传进来的是 Context<ContestEnv>，
+// 它比 AppEnv 多一个变量，而 Hono 的 Context 在 Variables 上是逆变的，写死会类型不兼容。
+export async function canAccessContest<E extends AppEnv>(
+  c: Context<E>,
   contest: ContestRow,
   checkType: "details" | "problems" | "ranks" | "submissions",
 ) {
@@ -62,6 +76,34 @@ export async function canAccessContest(
   return { ok: true as const }
 }
 
+/**
+ * 比赛内容路由的守卫中间件。旧后端用 `@check_contest_permission` 装饰器，漏挂一眼看得出来；
+ * 手工在 handler 里调 `canAccessContest` 则漏调一次就是静默放行，而且这类路由挂的是
+ * `optionalAuth`（本身不拦人），从路由注册那一行完全看不出它受保护。这个中间件把
+ * 「取比赛 → 404 → 鉴权 → 401/403」四步收进注册行里，恢复旧后端那种显眼程度。
+ *
+ * 通过后比赛对象放进 `c.var.contest`，handler 直接取，不必再查一次库。
+ *
+ * 注意：`POST /submissions` 用不了它 —— 那里的比赛 id 来自请求体而非路径参数，
+ * 中间件跑的时候还没解析 body。那一处仍是手工调用，见 submission.ts 内的说明。
+ */
+export function requireContestAccess(
+  checkType: "details" | "problems" | "ranks" | "submissions",
+  paramName = "id",
+): MiddlewareHandler<ContestEnv> {
+  return async (c, next) => {
+    const id = Number(c.req.param(paramName))
+    const contest = Number.isInteger(id) && id > 0 ? await findVisibleContest(id) : null
+    if (!contest) return failure(c, 404, "contest-not-found", "Contest does not exist")
+    const access = await canAccessContest(c, contest, checkType)
+    if (!access.ok) {
+      return failure(c, access.code === "login-required" ? 401 : 403, access.code, access.message)
+    }
+    c.set("contest", contest)
+    await next()
+  }
+}
+
 function ipv4Number(value: string) {
   const parts = value.split(".").map(Number)
   if (parts.length !== 4 || parts.some((part) => !Number.isInteger(part) || part < 0 || part > 255)) return null