GHSA-cpj3-3r2f-xj59 BIT-openbao-2026-33758 CVE-2026-33758 GO-2026-4862

OpenBao has Reflected XSS in its OIDC authentication error message

Medium Go

Severity: 0.0 / 10; Medium · CVSS 4.0
Exploit chance (EPSS): 0.30%; Chance of exploitation in the next 30 days. Higher than 22.54% of scored vulnerabilities.
Known exploited: No; Not in CISA's catalog
Weakness: CWE-20 Improper Input Validation; CWE-80 Improper Neutralization of Script-Related HTML Tags in a Web Page (Basic XSS)
Fix: 0.0.0-20260325133417-6e2b2dd84f0e; Upgrade github.com/openbao/openbao to this version or later

Description

Impact

OpenBao installations that have an OIDC/JWT authentication method enabled and a role with callback_mode=direct configured are vulnerable to XSS via the error_description parameter on the page for a failed authentication.

This allows an attacker access to the token used in the Web UI by a victim.

Patches

The error_description parameter has been replaced with a static error message in v2.5.2

Workarounds

The vulnerability can be mitigated by removing any roles with callback_mode set to direct.

Affected versions

Go

Package	Vulnerable	Fixed in
github.com/openbao/openbao	`< 0.0.0-20260325133417-6e2b2dd84f0e`	`0.0.0-20260325133417-6e2b2dd84f0e`

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

github.com/openbao/openbao Go → `0.0.0-20260325133417-6e2b2dd84f0e`

go

go get github.com/openbao/openbao@v0.0.0-20260325133417-6e2b2dd84f0e && go mod tidy

Severity breakdown

CVSS 4.0 0.0

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

Attack vector: Network
Attack complexity: Low
Attack requirements: None
Privileges required: None
User interaction: Passive
Confidentiality (vulnerable system): High
Integrity (vulnerable system): High
Availability (vulnerable system): High
Confidentiality (subsequent systems): High
Integrity (subsequent systems): High
Availability (subsequent systems): High

CVSS 3.1 6.1

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

Attack vector: Network
Attack complexity: Low
Privileges required: None
User interaction: Required
Scope: Changed
Confidentiality: Low
Integrity: Low
Availability: None

Weakness

CWE-20: Improper Input Validation

The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.

How to prevent it

Architecture and Design: Consider using language-theoretic security (LangSec) techniques that characterize inputs using a formal language and build "recognizers" for that language. This effectively requires parsing to be a distinct layer that effectively enforces a boundary between raw input and internal data representations, instead of allowing parser code to be scattered throughout the program, where it could be subject to errors or inconsistencies that create weaknesses. [REF-1109] [REF-1110] [REF-1111]
Architecture and Design: Use an input validation framework such as Struts or the OWASP ESAPI Validation API. Note that using a framework does not automatically address all input validation problems; be mindful of weaknesses that could arise from misusing the framework itself (CWE-1173).
Architecture and Design, Implementation: Understand all the potential areas where untrusted inputs can enter the product, including but not limited to: parameters or arguments, cookies, anything read from the network, environment variables, reverse DNS lookups, query results, request headers, URL components, e-mail, files, filenames, databases, and any external systems that provide data to the application. Remember that such inputs may be obtained indirectly through API calls.
Implementation: Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
Architecture and Design: For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server. Even though client-side checks provide minimal benefits with respect to server-side security, they are still useful. First, they can support intrusion detection. If the server receives input that should have been rejected by the client, then it may be an indication of an attack. Second, client-side error-checking can provide helpful feedback to the user about the expectations for valid input. Third, there may be a reduction in server-side processing time for accidental input errors, although this is typically a small savings.
Implementation: When your application combines data from multiple sources, perform the validation after the sources have been combined. The individual data elements may pass the validation step but violate the intended restrictions after they have been combined.
Implementation: Be especially careful to validate all input when invoking code that crosses language boundaries, such as from an interpreted language to native code. This could create an unexpected interaction between the language boundaries. Ensure that you are not violating any of the expectations of the language with which you are interfacing. For example, even though Java may not be susceptible to buffer overflows, providing a large argument in a call to native code might trigger an overflow.
Implementation: Directly convert your input type into the expected data type, such as using a conversion function that translates a string into a number. After converting to the expected data type, ensure that the input's values fall within the expected range of allowable values and that multi-field consistencies are maintained.
Implementation: Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180, CWE-181). Make sure that your application does not inadvertently decode the same input twice (CWE-174). Such errors could be used to bypass allowlist schemes by introducing dangerous inputs after they have been checked. Use libraries such as the OWASP ESAPI Canonicalization control. Consider performing repeated canonicalization until your input does not change any more. This will avoid double-decoding and similar scenarios, but it might inadvertently modify inputs that are allowed to contain properly-encoded dangerous content.
Implementation: When exchanging data between components, ensure that both components are using the same character encoding. Ensure that the proper encoding is applied at each interface. Explicitly set the encoding you are using whenever the protocol allows you to do so.

CWE-80: Improper Neutralization of Script-Related HTML Tags in a Web Page (Basic XSS)

The product receives input from an upstream component, but it does not neutralize or incorrectly neutralizes special characters such as "<", ">", and "&" that could be interpreted as web-scripting elements when they are sent to a downstream component that processes web pages.

How to prevent it

Implementation: Carefully check each input parameter against a rigorous positive specification (allowlist) defining the specific characters and format allowed. All input should be neutralized, not just parameters that the user is supposed to specify, but all data in the request, including hidden fields, cookies, headers, the URL itself, and so forth. A common mistake that leads to continuing XSS vulnerabilities is to validate only fields that are expected to be redisplayed by the site. We often encounter data from the request that is reflected by the application server or the application that the development team did not anticipate. Also, a field that is not currently reflected may be used by a future developer. Therefore, validating ALL parts of the HTTP request is recommended.
Implementation: Use and specify an output encoding that can be handled by the downstream component that is reading the output. Common encodings include ISO-8859-1, UTF-7, and UTF-8. When an encoding is not specified, a downstream component may choose a different encoding, either by assuming a default encoding or automatically inferring which encoding is being used, which can be erroneous. When the encodings are inconsistent, the downstream component might treat some character or byte sequences as special, even if they are not special in the original encoding. Attackers might then be able to exploit this discrepancy and conduct injection attacks; they even might be able to bypass protection mechanisms that assume the original encoding is also being used by the downstream component. The problem of inconsistent output encodings often arises in web pages. If an encoding is not specified in an HTTP header, web browsers often guess about which encoding is being used. This can open up the browser to subtle XSS attacks.
Implementation: With Struts, write all data from form beans with the bean's filter attribute set to true.
Implementation: To help mitigate XSS attacks against the user's session cookie, set the session cookie to be HttpOnly. In browsers that support the HttpOnly feature (such as more recent versions of Internet Explorer and Firefox), this attribute can prevent the user's session cookie from being accessible to malicious client-side scripts that use document.cookie. This is not a complete solution, since HttpOnly is not supported by all browsers. More importantly, XmlHttpRequest and other powerful browser technologies provide read access to HTTP headers, including the Set-Cookie header in which the HttpOnly flag is set.

References

Advisories

nvd.nist.gov/vuln/detail/CVE-2026-33758

Packages

github.com/openbao/openbao

Timeline

Mar 26, 2026 Published
Jul 27, 2026 Last updated by the source
Oct 31, 2026 Latest EPSS score

Advisory	Severity	Why it's related
GHSA-xp3c-3jw3-4vcr OpenBao Skips Stricter Deny Policy for LIST operations	Medium	Also affects github.com/openbao/openbao
GHSA-34fc-gh42-pj53 OpenBao's Recovery Mode Vulnerable To Token Leakage via Timing Attack	Critical	Also affects github.com/openbao/openbao
GHSA-444v-8vxr-p36h OpenBao Agent Writes Secrets to Stdout	Low	Also affects github.com/openbao/openbao
GHSA-59w7-v8rr-pr4p OpenBao's Templated Policies Allow Privilege Escalation via Wildcard Characters	High	Also affects github.com/openbao/openbao
GHSA-8w8f-r2xv-4q4j OpenBao: Transit secrets engine crashes on key creation with `derived: true` for asymmetric key types	Medium	Also affects github.com/openbao/openbao
GHSA-mwr2-wmgp-crj6 OpenBao's System Backend allows Unauthorized Management of the containing Namespace	Low	Also affects github.com/openbao/openbao
GHSA-c36x-h252-g9x2 OpenBao: Cross-namespace lease revocation/renewal via canonical sys/leases/{revoke,renew} — incomplete fix of CVE-2026-45808	Low	Also affects github.com/openbao/openbao
GHSA-6mwx-4547-5vc9 OpenBao: LDAPi ldaputil (wrong escape func)	Medium	Also affects github.com/openbao/openbao

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