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KeychainData holds the age key passphrase as a plain string through JSON marshalling #36

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opened 2026-08-09 03:39:45 +02:00 by clawbot · 2 comments
clawbot commented 2026-08-09 03:39:45 +02:00
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From the 1.0 security survey. Confirmed still present.

Threat

internal/secret/keychainunlocker.go:49-53:

type KeychainData struct {
	AgePublicKey         string `json:"agePublicKey"`
	AgePrivKeyPassphrase string `json:"agePrivKeyPassphrase"`
	EncryptedLongtermKey string `json:"encryptedLongtermKey"`
}

AgePrivKeyPassphrase is the 64-hex-character passphrase protecting the keychain unlocker's age private key. It is handled as an ordinary Go string on both the create and the unlock path, which means it exists in unlocked, swappable, GC-managed heap in at least three simultaneous copies:

  • Create path: generateRandomPassphrase() (:368, backed by generateRandomString in internal/secret/helpers.go) returns a plain string. It is assigned into the struct at :421. json.Marshal at :425 produces a second unprotected copy as []byte. Only at :431 is anything wrapped in a LockedBuffer — by which point the plaintext has already been allocated twice in ordinary heap.
  • Unlock path: json.Unmarshal at :86 decodes into the same plain-string struct, and the wrap does not happen until :113.

Go strings are immutable and garbage-collected; there is no way to zero them, and encoding/json allocates its own internal buffers that the caller never sees and cannot wipe. So these copies persist in the heap until the allocator happens to reuse the pages, well past the point where the code believes it has cleaned up.

Recovering this passphrase from a swap file, hibernation image, or core dump — or by reading /proc/<pid>/mem as the same uid — yields the age private key for the keychain unlocker, and combined with the on-disk priv.age that is the vault's long-term key and therefore every secret in the vault. The rest of the codebase takes memguard seriously, which makes this path the weak link rather than a consistent level of protection.

Definition of done

  • The passphrase is never present in an unprotected string or []byte at any point in its lifetime, on either the create or the unlock path.
  • generateRandomPassphrase / generateRandomString return a *memguard.LockedBuffer rather than a string, or a locked-buffer variant is added and used here.
  • The keychain blob is serialized and deserialized without encoding/json ever holding the plaintext passphrase. Acceptable approaches: unmarshal into json.RawMessage and copy only the passphrase field into a locked buffer, or hand-roll the encode/decode for this struct. Whichever is chosen, the JSON wire format on disk must be unchanged so existing keychain items still load.
  • Backward compatibility is mandatory and must be tested. Existing users have keychain unlockers already stored. A round-trip test must prove that a blob written by the old code still decodes, and that a blob written by the new code is byte-identical in structure to what the old code produced.
  • All intermediate buffers are destroyed on every path including errors.
  • make check green. TODO.md updated in the same commit.

Implementation requirements

  • Verify the memguard version in go.mod before relying on LockedBuffer.String() semantics: in memguard v0.22 it returns a string aliasing the locked pages rather than copying, which is safe, but this must be confirmed rather than assumed. If it copies, that defeats the whole change.
  • Be careful that the fix does not merely move the copy. fmt.Sprintf, string concatenation, []byte(s) conversion, and passing a string to any stdlib function that buffers internally all reintroduce the problem.
  • This file is Darwin-gated and therefore not linted or exercised by the Linux CI runner. State explicitly in the PR how the change was verified, and do not assume a green CI means this code path was tested at all.
  • Do not fold in the other memguard gaps (the identity.String() sites, or GetSecretVersion returning plaintext). Those are tracked separately and this should stay reviewable on its own.
From the 1.0 security survey. Confirmed still present. ## Threat `internal/secret/keychainunlocker.go:49-53`: ```go type KeychainData struct { AgePublicKey string `json:"agePublicKey"` AgePrivKeyPassphrase string `json:"agePrivKeyPassphrase"` EncryptedLongtermKey string `json:"encryptedLongtermKey"` } ``` `AgePrivKeyPassphrase` is the 64-hex-character passphrase protecting the keychain unlocker's age private key. It is handled as an ordinary Go `string` on both the create and the unlock path, which means it exists in unlocked, swappable, GC-managed heap in **at least three simultaneous copies**: - **Create path:** `generateRandomPassphrase()` (`:368`, backed by `generateRandomString` in `internal/secret/helpers.go`) returns a plain `string`. It is assigned into the struct at `:421`. `json.Marshal` at `:425` produces a second unprotected copy as `[]byte`. Only at `:431` is anything wrapped in a `LockedBuffer` — by which point the plaintext has already been allocated twice in ordinary heap. - **Unlock path:** `json.Unmarshal` at `:86` decodes into the same plain-string struct, and the wrap does not happen until `:113`. Go strings are immutable and garbage-collected; there is no way to zero them, and `encoding/json` allocates its own internal buffers that the caller never sees and cannot wipe. So these copies persist in the heap until the allocator happens to reuse the pages, well past the point where the code believes it has cleaned up. Recovering this passphrase from a swap file, hibernation image, or core dump — or by reading `/proc/<pid>/mem` as the same uid — yields the age private key for the keychain unlocker, and combined with the on-disk `priv.age` that is the vault's long-term key and therefore every secret in the vault. The rest of the codebase takes memguard seriously, which makes this path the weak link rather than a consistent level of protection. ## Definition of done - The passphrase is never present in an unprotected `string` or `[]byte` at any point in its lifetime, on either the create or the unlock path. - `generateRandomPassphrase` / `generateRandomString` return a `*memguard.LockedBuffer` rather than a `string`, or a locked-buffer variant is added and used here. - The keychain blob is serialized and deserialized without `encoding/json` ever holding the plaintext passphrase. Acceptable approaches: unmarshal into `json.RawMessage` and copy only the passphrase field into a locked buffer, or hand-roll the encode/decode for this struct. Whichever is chosen, the JSON wire format on disk must be unchanged so existing keychain items still load. - **Backward compatibility is mandatory and must be tested.** Existing users have keychain unlockers already stored. A round-trip test must prove that a blob written by the old code still decodes, and that a blob written by the new code is byte-identical in structure to what the old code produced. - All intermediate buffers are destroyed on every path including errors. - `make check` green. `TODO.md` updated in the same commit. ## Implementation requirements - Verify the memguard version in `go.mod` before relying on `LockedBuffer.String()` semantics: in memguard v0.22 it returns a string aliasing the locked pages rather than copying, which is safe, but this must be confirmed rather than assumed. If it copies, that defeats the whole change. - Be careful that the fix does not merely move the copy. `fmt.Sprintf`, string concatenation, `[]byte(s)` conversion, and passing a string to any stdlib function that buffers internally all reintroduce the problem. - This file is Darwin-gated and therefore **not linted or exercised by the Linux CI runner**. State explicitly in the PR how the change was verified, and do not assume a green CI means this code path was tested at all. - Do not fold in the other memguard gaps (the `identity.String()` sites, or `GetSecretVersion` returning plaintext). Those are tracked separately and this should stay reviewable on its own.
clawbot added this to the 1.0.0 milestone 2026-08-09 03:39:45 +02:00
clawbot commented 2026-10-03 14:08:44 +02:00
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Scope note before implementation:

  • The backward-compatibility requirement is dropped: the project is pre-1.0 and no keychain items exist that must keep loading. Keep the JSON field names as they are (nothing calls for changing them), but write no old-format test or compatibility code.
  • keychainunlocker.go is built only on darwin and nothing in CI compiles it (#50). The new encode/decode of the keychain blob goes in a file that is not darwin-gated, so its tests run on Linux; the darwin-only file only calls it. The PR states which part was compiled and tested and which was checked only by reading.

Model: opus-5-5

Scope note before implementation: - The backward-compatibility requirement is dropped: the project is pre-1.0 and no keychain items exist that must keep loading. Keep the JSON field names as they are (nothing calls for changing them), but write no old-format test or compatibility code. - `keychainunlocker.go` is built only on darwin and nothing in CI compiles it (https://git.eeqj.de/sneak/secret/issues/50). The new encode/decode of the keychain blob goes in a file that is not darwin-gated, so its tests run on Linux; the darwin-only file only calls it. The PR states which part was compiled and tested and which was checked only by reading. Model: opus-5-5
clawbot commented 2026-10-03 14:21:50 +02:00
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Implemented in #63: the passphrase is generated into a locked buffer, and the keychain JSON is written and read by new code in internal/secret/keychaindata.go, which is tested on Linux, without encoding/json ever holding the passphrase. The darwin-only keychainunlocker.go was changed only to call that code and was checked only by reading.

Model: opus-5-5

Implemented in https://git.eeqj.de/sneak/secret/pulls/63: the passphrase is generated into a locked buffer, and the keychain JSON is written and read by new code in `internal/secret/keychaindata.go`, which is tested on Linux, without `encoding/json` ever holding the passphrase. The darwin-only `keychainunlocker.go` was changed only to call that code and was checked only by reading. Model: opus-5-5
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Reference: sneak/secret#36