VulnerabilityPublished 21 Jul 2026

CVE-2026-57886: Gitea · Cross-repository issue/comment attachment re-linking can expose private attachment content

Affects code.gitea.io/giteaSource GCVE Database

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Mentioned vulnerabilities

CVE-2026-20736

Authoritative record:CVE-2026-57886· Medium 5.9

Not known to be exploited · CVSS 5.9 Medium : upgrade to 1.27.0 when convenient.

Data as of 30 Oct 2026, 11:52 UTC

CVSS 3.1 base score

5.9Medium

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

EPSS: 0.3% chance of exploitation in 30 days – higher than 24% 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:H/PR:L/UI:N/S:U/C:H/I:L/A:N

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

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: High: A successful attack depends on conditions beyond the attacker's control. That is, a successful attack cannot be accomplished at will, but requires the attacker to invest in some measurable amount of effort in preparation or execution against the vulnerable component before a successful attack can be expected. For example, a successful attack may require an attacker to: gather knowledge about the environment in which the vulnerable target/component exists; prepare the target environment to improve exploit reliability; or inject themselves into the logical network path between the target and the resource requested by the victim in order to read and/or modify network communications (e.g., a man in the middle attack).
Privileges Required: Low: The attacker is authorized with (i.e., requires) privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges may have the ability to cause an impact only to non-sensitive resources.
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: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
Integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 13 Aug 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
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

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), 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 Gitea's issue and comment attachment update paths accept attachment UUIDs without verifying that each attachment belongs to the target issue/comment repository. If an authenticated attacker knows a victim attachment UUID, they can re-link that attachment to an attacker-controlled issue or comment, causing later attachment access checks to use the attacker's repository authorization context. ## Affected - Component: web issue/comment attachment handling. - Confirmed version: `main` commit `a39b2775edcb3ba53def96794491b91335117d81` (`v1.27.0-dev-352-ga39b2775ed`). - Fixed in: not fixed at the time of validation. - Other versions: not exhaustively tested. The affected code path appears structurally similar to versions that contain the current issue/comment attachment update logic. ## Description / Root Cause `files[]` values from issue/comment edit flows are passed to `updateAttachments` in `routers/web/repo/issue.go:589-629`. That helper calls: - `models/issues/issue_update.go:267-278` (`UpdateIssueAttachments`) - `models/issues/comment.go:623-642` (`UpdateCommentAttachments`) Both functions load attachments by UUID and update the attachment linkage, but neither validates that the attachment row's `RepoID` matches the repository of the target issue/comment. They also do not reject attachments already linked to a different issue/comment. Attachment reads then use the linked issue/release repository to decide access: - `services/repository/repository.go:185-207` returns the repository ID from `IssueID` or `ReleaseID`. - `routers/web/repo/attachment.go:153-184` checks read permission on that linked repository. - `routers/web/repo/attachment.go:216-224` opens and serves the file from the attachment's storage path after the linked-repository permission check succeeds. For the global `/attachments/{uuid}` route in `routers/web/web.go:872-876`, there is no current repository context, so the early `attach.RepoID` mismatch check in `ServeAttachment` does not protect against this re-linking case. A patched sibling path already demonstrates the intended invariant: `models/repo/release.go:179-215` rejects release attachments whose `RepoID` differs from the release repository. That guard was introduced for CVE-2026-20736, but the issue/comment paths still lack an equivalent check. ## Impact An attacker who can edit an issue/comment in a repository they can read can move a known victim attachment UUID into that repository's authorization context. After the re-link, the attachment download path resolves access against the attacker-controlled repository while serving the original attachment file. This can disclose private issue/comment attachments if the attacker has obtained the UUID through prior legitimate access, copied links, notification content, logs, browser history, or another exposure. The attack does not require write access to the victim repository. ## Reproduction Summary Full HTTP/E2E observation: - A local Gitea server was started with an isolated SQLite database. - A victim user created private repositories, private issues, and issue attachments containing unique marker strings. - An attacker user first attempted to download each victim attachment through `/attachments/{uuid}` and received `404`. - The attacker then submitted the victim UUID through the real issue edit route in an attacker-controlled public repository. - The same attacker could then download the victim issue attachment through `/attachments/{uuid}` and received `200`; the response body contained the unique issue marker. - The attacker repeated the flow through the real comment edit route and could download the second victim attachment with `200`; the response body contained the unique comment marker. Model-level issue-path behavior: - A fixture attachment with `RepoID = 2` and `IssueID = 4` was passed to `UpdateIssueAttachments` for attacker issue `ID = 1`, whose `RepoID = 1`. - The call succeeded. - The attachment row still had `RepoID = 2`, but its `IssueID` was changed to the attacker issue. - `GetAttachmentLinkedTypeAndRepoID` then resolved the attachment to attacker repository `RepoID = 1`. Model-level comment-path behavior: - The same cross-repository attachment UUID was passed to `UpdateCommentAttachments` for attacker comment `ID = 1`. - The call succeeded. - The attachment row still had `RepoID = 2`, but its `IssueID` and `CommentID` were changed to the attacker's issue/comment. - The linked repository used for access checks became attacker repository `RepoID = 1`. Negative control: - Existing release test `TestAddReleaseAttachmentsRejectsDifferentRepo` passes and confirms the release path rejects the same class of cross-repository attachment linkage. Detailed verifier and step-by-step runbook are available on request. ## Suggested Fix Add repository and linkage validation before updating issue/comment attachments. Recommended checks: - Load the target issue for `UpdateIssueAttachments` and deri

CWE-639Authorization Bypass Through User-Controlled Key (opens in a new tab)
Base weaknessLikelihood of exploit: HighCWE Top 25 (2025): #24OWASP Top 10 A01:2025: Broken Access Control (opens in a new tab)
The system's authorization functionality does not prevent one user from gaining access to another user's data or record by modifying the key value identifying the data.
Architecture and Design
For each and every data access, ensure that the user has sufficient privilege to access the record that is being requested.
Architecture and Design · Implementation
Make sure that the key that is used in the lookup of a specific user's record is not controllable externally by the user or that any tampering can be detected.
Architecture and Design
Use encryption in order to make it more difficult to guess other legitimate values of the key or associate a digital signature with the key so that the server can verify that there has been no tampering.
OWASP Cheat Sheets
Access Control (opens in a new tab)
Authorization Testing Automation (opens in a new tab)
Cross-Site Request Forgery Prevention (opens in a new tab)
Insecure Direct Object Reference Prevention (opens in a new tab)
Authorization (opens in a new tab)
OWASP ASVS 4.0.3
V4.1.2 (opens in a new tab)
V4.2.1 (opens in a new tab)
V8.3.8 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).
CWE-862Missing Authorization (opens in a new tab)
Class weaknessLikelihood of exploit: HighCWE Top 25 (2025): #4OWASP Top 10 A01:2025: Broken Access Control (opens in a new tab)
The product does not perform an authorization check when an actor attempts to access a resource or perform an action.
Architecture and Design
Divide the product into anonymous, normal, privileged, and administrative areas. Reduce the attack surface by carefully mapping roles with data and functionality. Use role-based access control (RBAC) to enforce the roles at the appropriate boundaries.
Architecture and Design
Ensure that access control checks are performed related to the business logic. These checks may be different than the access control checks that are applied to more generic resources such as files, connections, processes, memory, and database records.
Architecture and Design · Libraries or Frameworks
Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
OWASP Cheat Sheets
Authorization (opens in a new tab)
OWASP ASVS 4.0.3
V8.3.8 (opens in a new tab)
V13.4.2 (opens in a new tab)
V7.2.2 (opens in a new tab)
Attack patterns
Exploitation of Thunderbolt Protection Flaws (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Affected software

Description

WeaknessesCWE-639, CWE-862

Technical details

References

Community reviews

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