CVE-2026-58436

ParseAcceptLanguage quadratic-time DoS via Locale middleware on unauthenticated requests

ParseAcceptLanguage quadratic-time DoS via Locale middleware on unauthenticated requests

Summary

The Locale middleware that runs in front of every unauthenticated request calls golang.org/x/text/language.ParseAcceptLanguage on the raw Accept-Language header without imposing a size or shape filter. The underlying parser has quadratic-time behaviour on long lists of malformed language tags. The CVE-2022-32149 guard that golang.org/x/text added in v0.3.8 caps the number of - characters in the input at 1000, but it does not cap _ characters even though the parser's internal scanner aliases _ to - before parsing. A single unauthenticated GET request with an Accept-Language header built out of _ separators burns ~2 seconds of server CPU on the host running Gitea; ten concurrent attackers saturate a ten-core box for the duration of the attack while consuming ~1 MiB of upstream bandwidth per request.

Affected versions

code.gitea.io/gitea 1.22.6 and (per code inspection of main) all earlier and later 1.22.x / 1.23.x / 1.24.x / 1.25.x / 1.26.x versions that do not impose their own size limit on the Accept-Language header before calling ParseAcceptLanguage. Verified on:

• the official gitea/gitea:1.22.6 docker image (E2E below)
• main at commit 6f4027a6be28c876c0abaf37cc939658645b78a3 by reading modules/web/middleware/locale.go (the call site at line 38 is unchanged on main)

Privilege required

Unauthenticated. The Locale middleware runs for every HTTP request including the landing page and the sign-in page.

Vulnerable code

modules/web/middleware/locale.go:38 (blob SHA fc396f0808187c358b4fc15dcefcd6957140a780):

// 3. Get language information from 'Accept-Language'.
// The first element in the list is chosen to be the default language automatically.
if len(lang) == 0 {
    tags, _, _ := language.ParseAcceptLanguage(req.Header.Get("Accept-Language"))
    tag := translation.Match(tags...)
    lang = tag.String()
}

req.Header.Get("Accept-Language") is the unfiltered HTTP header. Default Go net/http MaxHeaderBytes is 1 << 20 = 1 MiB and Gitea does not override it, so the parser is allowed to receive up to a megabyte of attacker-controlled data.

CVE-2022-32149 hardened ParseAcceptLanguage by counting - characters and rejecting inputs with more than 1000 of them. The guard does not count _ characters even though the scanner converts _ to - at parse time (golang.org/x/text/internal/language/parse.go). A 1 MiB header full of 9-character _aaaaaaaaa_aaaaaaaaa_... tokens contains zero - characters, passes the guard, and then drives the scanner into the O(N²) gobble path. The fix author of CVE-2022-32149 treated - as the canonical separator; the _ alias was added in 2013, nine years before the fix.

How Accept-Language reaches ParseAcceptLanguage

Every Gitea HTTP request passes through Locale as it is wired up via the global request pipeline (Gitea registers the middleware on its router in routers/web/web.go). The middleware sequence is:

1. The request enters Locale(resp, req).
2. req.URL.Query().Get("lang") returns "" (attacker omits lang).
3. req.Cookie("lang") returns nil on a fresh client (attacker uses a fresh client, or simply does not send the cookie).
4. req.Header.Get("Accept-Language") returns the full attacker-supplied header value.
5. language.ParseAcceptLanguage(...) runs unfiltered.

No size or character class filter is applied between (4) and (5).

Proof of concept

Single-line bash reproducer that crafts the malicious header and times one request against a fresh gitea/gitea:1.22.6 container:

docker run -d --name gitea --rm -p 13000:3000 gitea/gitea:1.22.6
sleep 8

PAYLOAD="en$(python3 -c 'print("_abcdefghi" * 100000, end="")')"
echo "header size = ${#PAYLOAD} bytes"

curl -sS…

ParseAcceptLanguage quadratic-time DoS via Locale middleware on unauthenticated requests

ParseAcceptLanguage quadratic-time DoS via Locale middleware on unauthenticated requests

Summary

The Locale middleware that runs in front of every unauthenticated request calls golang.org/x/text/language.ParseAcceptLanguage on the raw Accept-Language header without imposing a size or shape filter. The underlying parser has quadratic-time behaviour on long lists of malformed language tags. The CVE-2022-32149 guard that golang.org/x/text added in v0.3.8 caps the number of - characters in the input at 1000, but it does not cap _ characters even though the parser's internal scanner aliases _ to - before parsing. A single unauthenticated GET request with an Accept-Language header built out of _ separators burns ~2 seconds of server CPU on the host running Gitea; ten concurrent attackers saturate a ten-core box for the duration of the attack while consuming ~1 MiB of upstream bandwidth per request.

Affected versions

code.gitea.io/gitea 1.22.6 and (per code inspection of main) all earlier and later 1.22.x / 1.23.x / 1.24.x / 1.25.x / 1.26.x versions that do not impose their own size limit on the Accept-Language header before calling ParseAcceptLanguage. Verified on:

• the official gitea/gitea:1.22.6 docker image (E2E below)
• main at commit 6f4027a6be28c876c0abaf37cc939658645b78a3 by reading modules/web/middleware/locale.go (the call site at line 38 is unchanged on main)

Privilege required

Unauthenticated. The Locale middleware runs for every HTTP request including the landing page and the sign-in page.

Vulnerable code

modules/web/middleware/locale.go:38 (blob SHA fc396f0808187c358b4fc15dcefcd6957140a780):

// 3. Get language information from 'Accept-Language'.
// The first element in the list is chosen to be the default language automatically.
if len(lang) == 0 {
    tags, _, _ := language.ParseAcceptLanguage(req.Header.Get("Accept-Language"))
    tag := translation.Match(tags...)
    lang = tag.String()
}

req.Header.Get("Accept-Language") is the unfiltered HTTP header. Default Go net/http MaxHeaderBytes is 1 << 20 = 1 MiB and Gitea does not override it, so the parser is allowed to receive up to a megabyte of attacker-controlled data.

CVE-2022-32149 hardened ParseAcceptLanguage by counting - characters and rejecting inputs with more than 1000 of them. The guard does not count _ characters even though the scanner converts _ to - at parse time (golang.org/x/text/internal/language/parse.go). A 1 MiB header full of 9-character _aaaaaaaaa_aaaaaaaaa_... tokens contains zero - characters, passes the guard, and then drives the scanner into the O(N²) gobble path. The fix author of CVE-2022-32149 treated - as the canonical separator; the _ alias was added in 2013, nine years before the fix.

How Accept-Language reaches ParseAcceptLanguage

Every Gitea HTTP request passes through Locale as it is wired up via the global request pipeline (Gitea registers the middleware on its router in routers/web/web.go). The middleware sequence is:

1. The request enters Locale(resp, req).
2. req.URL.Query().Get("lang") returns "" (attacker omits lang).
3. req.Cookie("lang") returns nil on a fresh client (attacker uses a fresh client, or simply does not send the cookie).
4. req.Header.Get("Accept-Language") returns the full attacker-supplied header value.
5. language.ParseAcceptLanguage(...) runs unfiltered.

No size or character class filter is applied between (4) and (5).

Proof of concept

Single-line bash reproducer that crafts the malicious header and times one request against a fresh gitea/gitea:1.22.6 container:

docker run -d --name gitea --rm -p 13000:3000 gitea/gitea:1.22.6
sleep 8

PAYLOAD="en$(python3 -c 'print("_abcdefghi" * 100000, end="")')"
echo "header size = ${#PAYLOAD} bytes"

curl -sS…

Gitea: ParseAcceptLanguage quadratic-time DoS via Locale middleware on unauthenticated requests in gitea.dev

This update for govulncheck-vulndb fixes the following issues:

• Update to version 0.0.20260723T184607 2026-07-23T18:46:07Z (jsc#PED-11136).

Go CVE Numbering Authority IDs added or updated with aliases:

• GO-2026-4730 CVE-2026-33022 GHSA-cv4x-93xx-wgfj
• GO-2026-4761 CVE-2026-33211 GHSA-j5q5-j9gm-2w5c
• GO-2026-5102 CVE-2026-45021 GHSA-3vcp-chfh-f6r2
• GO-2026-5272 CVE-2026-40938 GHSA-94jr-7pqp-xhcq
• GO-2026-5486 CVE-2026-40924 GHSA-m2cx-gpqf-qf74
• GO-2026-5542 CVE-2026-40090 GHSA-pj97-4p9w-gx3q
• GO-2026-5630 CVE-2026-25542 GHSA-rmx9-2pp3-xhcr
• GO-2026-5643 CVE-2026-40923 GHSA-rx35-6rhx-7858
• GO-2026-5675 CVE-2026-41492 GHSA-vvf7-6rmr-m29q
• GO-2026-5711 CVE-2026-40161 GHSA-wjxp-xrpv-xpff
• GO-2026-5746 CVE-2026-41567 GHSA-x86f-5xw2-fm2r
• GO-2026-5749 CVE-2026-41328 GHSA-x92x-px7w-4gx4
• GO-2026-5837 CVE-2026-44840 GHSA-q2m9-6jp9-c6mc
• GO-2026-5929 CVE-2026-44342 GHSA-26v7-h57m-gh9m
• GO-2026-5930 CVE-2026-33655 GHSA-6qcr-qxgr-m7fv
• GO-2026-5933 GHSA-3g4q-2f67-2gvh
• GO-2026-5934 GHSA-59qp-cfj3-rp64
• GO-2026-5935 GHSA-7856-g3gv-9wq8
• GO-2026-5936 CVE-2026-53552 GHSA-26rh-24rg-j3vv
• GO-2026-5937 CVE-2026-53508 GHSA-2jcc-mxv7-p3f9
• GO-2026-5938 CVE-2026-53553 GHSA-4g5x-hcwm-82jw
• GO-2026-5939 CVE-2026-10517 GHSA-698x-9w2p-7vvp
• GO-2026-5940 CVE-2026-53572 GHSA-6w3m-4hhp-775q
• GO-2026-5941 CVE-2026-53487 GHSA-gvhc-wv3v-7pf8
• GO-2026-5942 CVE-2026-46600
• GO-2026-5944 CVE-2026-50197 GHSA-659f-rgp5-w4wf
• GO-2026-5945 CVE-2026-6815 GHSA-rmxx-v9rj-vpvg
• GO-2026-5946 CVE-2026-52831 GHSA-v5px-423j-pf7p
• GO-2026-5947 CVE-2026-53649 GHSA-xqhv-chqm-fhcc
• GO-2026-5948 CVE-2026-50554 GHSA-588f-fvcv-xhvf
• GO-2026-5949 CVE-2026-50553 GHSA-rqrh-8wpv-x7hh
• GO-2026-5950 CVE-2026-53602 GHSA-339v-266x-79xr
• GO-2026-5951 CVE-2026-10219 GHSA-6jm8-4fhr-5w64
• GO-2026-5952 CVE-2026-49834 GHSA-9vcr-p3rj-q5q6
• GO-2026-5953 CVE-2026-9094 GHSA-c9w5-qp6m-m395
• GO-2026-5956 CVE-2026-55252 GHSA-h5g6-xmh4-hc37
• GO-2026-5957 CVE-2026-54158 GHSA-5xfx-xj4h-5p7r
• GO-2026-5958 CVE-2026-54068 GHSA-gcm7-57gf-953c
• GO-2026-5959 CVE-2026-54072 GHSA-h29v-hj44-q8cv
• GO-2026-5961 CVE-2026-54069 GHSA-hvr9-72v2-fff3
• GO-2026-5962 CVE-2026-54088 GHSA-m93h-4hw7-5qcm
• GO-2026-5963 CVE-2026-54067 GHSA-mvjr-vv3c-w4qv
• GO-2026-5964 CVE-2026-54066 GHSA-p4m3-mgmm-c664
• GO-2026-5965 CVE-2026-54070 GHSA-w7cg-whh7-xp28
• GO-2026-5966 CVE-2026-54089 GHSA-xqp3-jq6g-x3qm
• GO-2026-5967 CVE-2026-50551 GHSA-56mp-4f3v-fgj2
• GO-2026-5968 CVE-2026-54174 GHSA-fpg8-7664-jc5q
• GO-2026-5969 GHSA-g936-7jqj-mwv8
• GO-2026-5970 CVE-2026-56852
• GO-2026-5973 CVE-2026-54250 GHSA-jxr7-mqhw-9p98
• GO-2026-5974 CVE-2026-44300 GHSA-wmj8-9953-vff5
• GO-2026-5975 CVE-2026-50018 GHSA-42j2-w334-qxw7
• GO-2026-5976 CVE-2026-50141 GHSA-g7mm-9vx7-jm7h
• GO-2026-5977 CVE-2026-50013 GHSA-qrh4-p6v4-mrfg
• GO-2026-5978 CVE-2026-50125 GHSA-qw5r-ppcg-f8rj
• GO-2026-5979 CVE-2026-50006 GHSA-xrcf-6jh3-ggvx
• GO-2026-5980 CVE-2026-50158 GHSA-2c7f-fxww-6w6c
• GO-2026-5981 GHSA-mqxv-9rm6-w8qc
• GO-2026-5982 GHSA-pqg7-v6wh-3pfp
• GO-2026-5984 CVE-2026-53604 GHSA-2p2f-px33-4vv5
• GO-2026-5985 GHSA-7rx3-5wx3-5v76
• GO-2026-5986 CVE-2026-61699 GHSA-cm26-5974-52h8
• GO-2026-5987 CVE-2026-55513 GHSA-g4x6-jcvr-9m3g
• GO-2026-5988 CVE-2026-54628 GHSA-hwrq-8wxh-q4xv
• GO-2026-5989 CVE-2026-55512 GHSA-m3cx-mwpg-32jg
• GO-2026-5990 CVE-2026-54629 GHSA-mf78-3rpf-r784
• GO-2026-5991 CVE-2026-53603 GHSA-q4vm-pq3q-8wgq
• GO-2026-5992 CVE-2026-61549 GHSA-qf34-295c-26v8
• GO-2026-5996 CVE-2026-54450 GHSA-pph6-vfjv-vpjw
• GO-2026-5997 CVE-2026-54452 GHSA-xgch-x3mx-cm3c
• GO-2026-5998 CVE-2026-54495 GHSA-398h-7f66-3h4p
• GO-2026-5999 CVE-2026-10814 GHSA-jh6h-v6mp-h22v
• GO-2026-6002 CVE-2026-58196 GHSA-pr64-jmmf-jp54
• GO-2026-6003 CVE-2026-53714 GHSA-22xc-xg2r-9j7v
• GO-2026-6004 CVE-2026-52833 GHSA-3v79-m2cg-89ww
• GO-2026-6005 CVE-2026-53715 GHSA-8fv2-88gg-hm7q
• GO-2026-6006 CVE-2026-53716 GHSA-cxpq-8v7q-cg56 *…