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Response snapshot Oct 27, 2026, 05:58 UTC

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VulnerabilityCVE-2026-111755

follow-redirects sensitiveHeaders regex escaping can expose credential headers

```js this._headerFilter = new RegExp("^(?:" + sensitiveHeaders.concat(options.sensitiveHeaders).map(escapeRegex).join("|") + ")$", "i"); ``` `escapeRegex` at `index.js:703-705`:

Published Updated

At a glance

Exploited
Not known
Severity
8.2 High (CVSS 4.0)
Chance of exploitation
0.5% in the next 30 days
Sources
2 independent sources

What to do

GitHub lists first patched versions: follow-redirects: 1.16.1. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-8r9p-f939-6h3c (opens a new tab)

What happened

### Summary follow-redirects 1.16.0 introduced the `sensitiveHeaders` option (the fix for CVE-2026-40895 / GHSA-r4q5-vmmm-2653), which lets an application declare extra header names that must be removed when a redirect crosses to a different host or downgrades protocol.

The filter is a single case-insensitive regular expression built by concatenating the declared header names into an alternation after passing each through `escapeRegex`. `escapeRegex` escapes only a partial set of metacharacters and leaves `^`, `|`, `[`, `{`, and `}` unescaped.

Header names may legitimately contain `^` and `|` (both are valid RFC 9110 token characters that Node accepts and sends), and for a declared name containing either, the generated pattern can never match the intended header.

As a result, an application that adopts this option to protect a custom credential header, then follows an attacker-controlled cross-origin redirect, forwards that credential to the attacker with no error or warning, while believing it is protected. The failure is silent: the protection simply does not exist for the affected names.

Continue reading

The built-in list (Authorization, Proxy-Authorization, Cookie) contains no metacharacters and is not affected by this defect.

### Details The filter is constructed once, in the `RedirectableRequest` constructor at `index.js:118-120`:

```js this._headerFilter = new RegExp("^(?:" + sensitiveHeaders.concat(options.sensitiveHeaders).map(escapeRegex).join("|") + ")$", "i"); ```

`escapeRegex` at `index.js:703-705`:

```js function escapeRegex(regex) { return regex.replace(/[\]\\/()*+?.$]/g, "\\$&"); // escapes ] \ / ( ) * + ? . $ -- NOT ^ | [ { } } ```

The character class escapes `]`, `\`, `/`, `(`, `)`, `*`, `+`, `?`, `.`, and `$`. It omits `^`, `|`, `[`, `{`, and `}`. Of these, Node's `http.ClientRequest` accepts `^` and `|` in header names (they are valid `tchar` values under RFC 9110) and rejects `[`, `{`, `}` with `ERR_INVALID_HTTP_TOKEN`, so `^` and `|` are the reachable vectors for a silent credential leak.

Separately, although `[`, `{`, `}` cannot appear as live header names, declaring a `sensitiveHeaders` entry that contains one of them injects an unbalanced token into the alternation (for example an unterminated character class), so the filter `RegExp` throws a `SyntaxError` in the `RedirectableRequest` constructor and the request fails to start.

That case is a loud request-time crash from the same incomplete-escaping root cause rather than a silent bypass, and the canonical escaper below fixes it as well.

For a declared sensitive header name containing an unescaped metacharacter, the alternation is broken in a fail-open way:

- A name containing `^`, for example `X-Api^Key`, yields the alternative `X-Api^Key` inside the pattern. The `^` becomes a mid-pattern start-of-string anchor, so the alternative can never match any real header name. `test("X-Api^Key")` returns `false`, and the header is not stripped. - A name containing `|`, for example `X-Token|Secret`, is split into two separate alternatives `X-Token` and `Secret`.

The real header `X-Token|Secret` is never matched (not stripped), while unrelated headers literally named `X-Token` or `Secret` would be stripped instead.

The generated filter source, reproduced from the exact library logic, is: ``` ^(?:Authorization|Proxy-Authorization|Cookie|X-Api^Key|X-Token|Secret|X-Control-Key)$ ``` Direct matching results against this filter: `X-Api^Key` -> false, `X-Token|Secret` -> false, `X-Control-Key` (normal name) -> true, and the split-off `X-Token` -> true and `Secret` -> true (collateral wrong-stripping). The built-ins Authorization, Proxy-Authorization, Cookie all -> true.

Secondary, related weakness (filter snapshot not refreshed after `beforeRedirect`): the filter is built once at construction and applied at `index.js:490`, which runs before the `beforeRedirect(this._options, ...)` hook and the subsequent `_sanitizeOptions` at `index.js:494-506`. Because the strip happens before the hook and `this._headerFilter` is never rebuilt, any entry a caller adds to `options.

sensitiveHeaders` inside `beforeRedirect` is silently ignored. This facet is lower severity: mutating `sensitiveHeaders` inside `beforeRedirect` is not a documented usage of the option (the documented path is the request option), so it is best treated as a hardening item bundled with the escaping fix rather than an independent control bypass.

It is included here because both issues undermine the same control and share a remediation.

Suggested remediation: two changes close both facets.

1. Escape the complete set of regular-expression metacharacters: ```js function escapeRegex(str) { return str.replace(/[.*+?^${}()|[\]\\]/g, "\\$&"); } ``` This was verified to restore correct matching for all affected names while preserving the built-in matches.

2. Build the filter at strip time, or rebuild it after the `beforeRedirect` hook re-sanitizes options, so entries added inside the hook take effect. For example, replace the cached `this._headerFilter` with a `this._getHeaderFilter()` that constructs the RegExp from the current `this._options.sensitiveHeaders` on each redirect.

Additionally, since header names have a strict grammar, consider validating each entry of `options.sensitiveHeaders` against the RFC 9110 token character set and throwing an explicit error on invalid names, so misconfiguration fails loudly. Add a unit test asserting that every declared name is actually matched by the generated filter; the current suite only exercises metacharacter-free names (`Sensitive-A`, `x-sensitive-b`), which is why the defect passes CI.

References: - https://github.com/follow-redirects/follow-redirects/security/advisories/GHSA-r4q5-vmmm-2653 - https://github.com/follow-redirects/follow-redirects/pull/284 - https://github.com/follow-redirects/follow-redirects/commit/844c4d302ac963d29bdb5dc1754ec7df3d70d7f9

### PoC Environment: Node.js v24.18.0 on Windows 11. Run each script from a c

Affected package ranges reported by GitHub: follow-redirects: >= 1.16.0, < 1.16.1

Scores and how they were measured

CVSS base severity

8.2

Version 4.0As of

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

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

0.5%

Scored Percentile 40.5%

Model and measurement source (opens a new tab)

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-8r9p-f939-6h3c (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-8r9p-f939-6h3c, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  3. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-8r9p-f939-6h3c, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  4. Primary source

    NVD CVE-2026-111755 (opens a new tab)

    NVD record: description, CVSS (the CNA score is preferred), affected products, and publication date. Not evidence of exploitation.

    Published Checked

  5. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

  6. Primary source

    FIRST measured EPSS score (opens a new tab)

    Measured EPSS probability and percentile for CVE-2026-111755, scored 2026-10-26. This is a model estimate, not proof of exposure.

    Published Checked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, October 20). follow-redirects sensitiveHeaders regex escaping can expose credential headers (CVE-2026-111755). https://kevwire.com/record/CVE-2026-111755

MLA

"follow-redirects sensitiveHeaders regex escaping can expose credential headers (CVE-2026-111755)." KEVWire, 20 Oct. 2026, kevwire.com/record/CVE-2026-111755.

Chicago

KEVWire. "follow-redirects sensitiveHeaders regex escaping can expose credential headers (CVE-2026-111755)." Last modified October 20, 2026. https://kevwire.com/record/CVE-2026-111755.

Evidence summary (plain text)

follow-redirects sensitiveHeaders regex escaping can expose credential headers (Oct 20, 2026).
```js
this._headerFilter = new RegExp("^(?:" +
 sensitiveHeaders.concat(options.sensitiveHeaders).map(escapeRegex).join("|") +
 ")$", "i");
```

`escapeRegex` at `index.js:703-705`:
CVSS 8.2 (version 4.0; evidence as of Oct 20, 2026; https://github.com/advisories/GHSA-8r9p-f939-6h3c).
EPSS 0.5% for the following 30 days, scored Oct 26, 2026 (https://api.first.org/data/v1/epss?cve=CVE-2026-111755&date=2026-10-26).
Sources:
GitHub-reviewed advisory GHSA-8r9p-f939-6h3c: https://github.com/advisories/GHSA-8r9p-f939-6h3c
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMVQyMDozMDoyNlrOAAfvxw%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMVQyMDowMzo1N1rOAAfvxQ%3D%3D
NVD CVE-2026-111755: https://nvd.nist.gov/vuln/detail/CVE-2026-111755
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?pubStartDate=2026-10-12T13:35:55.142Z&pubEndDate=2026-10-26T13:35:55.142Z&resultsPerPage=500&startIndex=5500
FIRST measured EPSS score: https://api.first.org/data/v1/epss?cve=CVE-2026-111755&date=2026-10-26
Record ID: CVE-2026-111755.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Oct 27, 2026, 01:40 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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