CVE-2026-32953

EUVD-2026-13545 · Published Mar 17, 2026

Tillitis TKey Client has an Error in Protocol Implementation

Impact

Some specific (1 out of 256) User Supplied Secrets (USS) were not used,
making the resulting Compound Device Identifier (CDI) the same as if no
USS was provided.

Affected client applications: all client apps using the
tkeyclient Go module.

Patches

Upgrade to v1.3.0.

NOTE WELL: For the affected end users upgrading an app containing
tkeyclient to v1.3.0 means their key material will change. An end
user can get their old keys by not entering any USS. Please make sure
to communicate this to end users.

Affected users

The steps required to assess whether your USS is vulnerable may vary
depending on the client application. The example below shows how to
perform the check using tkey-ssh-agent and the known vulnerable USS
adl.

Insert the TKey into the client
Run tkey-ssh-agent -p --uss
When prompted for a User Supplied Secret, enter adl
Note the public key and call it pubkey-with-uss
Remove the TKey from the client
Insert the TKey into the client again
Run tkey-ssh-agent -p
Note the public key and call it pubkey-without-uss

Expected behavior:
pubkey-with-uss and pubkey-without-uss should not be equal.

Observed behavior:
pubkey-with-uss and pubkey-without-uss are equal.

Workaround

We recommend everyone using tkeyclient to update to v1.3.0 and
release new versions of the client apps using it.

However, end users that are unable to upgrade to a new version of a client
app, the recommendation is to change to an unaffected USS. Include
specific instructions for your client app.

Details

When loading the device app an optional 32 bytes USS digest is also
sent. The intention is to ask the end user to enter a USS of arbitrary
length, hash it, and then send a 32 bytes digest to TKey.

However, there was a bug when sending the digest from the client. The
index in the outgoing buffer is wrong and overwrites the boolean
defining if the USS is used or not.

This means that if the USS digest begins with a 0, the rest of the
digest is not used at all. If it begins with something else, setting
the boolean to true, the USS is used.

The exported LoadApp() function calls an internal helper function
loadApp() which contains this code:

  if len(secretPhrase) == 0 {
    tx[6] = 0
  } else {
    tx[6] = 1 // Note the 6 here
    // Hash user's phrase as USS
    uss := blake2s.Sum256(secretPhrase)
    copy(tx[6:], uss[:]) // Note that 6 is used again
  }

A side effect of this behavior is that only 31 bytes of the USS are
used. This is not considered a security issue, but an option has been
added to enforce use of the full USS. See the release notes for
details. To avoid forcing all users to roll their keys, this option is
disabled by default and must be explicitly enabled.

The fix

The fix focuses on solving the vulnerability only by: 1) use correct
index, 2) always use the last 31 bytes of the USS:

  if len(secretPhrase) == 0 {
    tx[6] = 0
  } else {
    tx[6] = 1
    // Hash user's phrase as USS
    uss := blake2s.Sum256(secretPhrase)
    copy(tx[7:], uss[1:])
  }

This change means the key material of affected end users will change
compared to earlier versions of tkeyclient. They have the choice of:

Not using a USS and keep their keys.
Keep using their USS and use new generated keys.
Use another USS and thus new keys.

Technologies

Tillitis Tkey ClientTillitis Tkeyclient

Weaknesses

CWE-303

References

Potentially impacted assets

See if this affects your attack surface

Latest trending attack

Criticalyesterday

Google Brotli decoder - Remote Code Execution via compressed requests (Exploitation Check)

This control is the second step of the Patrowl response to CVE-2026-111497 (Node2Shell). It complements the first control of 22 October 2026, which focused on the Node.js runtime, and does not replace it. Why a second control CVE-2026-111497 is an out-of-bounds write in the Google Brotli decoder, the library that decompresses Brotli ("br") data. It was first published as a Node.js vulnerability, because Node.js bundles this decoder. Later publications showed that the flaw is in the library itself. Every product that embeds an affected version of the decoder is concerned, whatever its language or vendor. A public proof of concept demonstrates code execution. Any server that decompresses request bodies sent with "Content-Encoding: br" exposes the decoder to unauthenticated attackers. Known cases include Express 5 and NestJS 11 on Node.js, Koa and Fastify setups, Bun, Envoy and Istio with request decompression enabled, and any application or reverse proxy that decodes Brotli request bodies with an affected library. The flaw also works in the other direction. A malicious server can compromise an unpatched client that decodes a Brotli response, for example Node.js fetch(), Python clients (requests, httpx, aiohttp, Scrapy) with the Brotli or brotlicffi package, or libcurl builds with Brotli support. What this control checks Patrowl sends small, valid Brotli-compressed requests to each asset and observes whether the server decodes them. The check does not depend on the technology: it detects the behaviour, whatever the stack behind it. These requests are what any legitimate client could send. They never reach the vulnerable code path and cannot affect the availability of the service. How to read the result Potentially impacted means the asset decodes Brotli request bodies: the attack surface is exposed. It does not confirm that the asset is vulnerable. The version of the Brotli decoder in use is not visible from the outside. This check covers applications that parse request bodies on their root path. A Not impacted result does not rule out exposure on other routes, nor on the client side. Checking the versions on the servers remains the only exhaustive verification. Two situations are possible. When the decoding is done by your own application or reverse proxy, identify the component and update it. If an update is not possible right away, reject requests with "Content-Encoding: br" at the reverse proxy or WAF. When the asset is hosted on a managed platform or behind a CDN (for example Platform.sh, Upsun or Fastly), the decoding may be done by the provider's edge router, in front of your application. You cannot patch it yourself, but this router handles all the traffic of your site. Ask your provider to confirm that its edge components are patched against CVE-2026-111497. Assets hosted on a managed platform or behind a CDN carry the tag "paas: platform.sh" or "cdn: fastly" in the asset view: for these assets, the Brotli decoding is done by the provider's edge router, in front of your application, and only the provider can patch it. Affected and fixed versions Google Brotli 1.0.3 to 1.2.0 are affected, fixed in 1.0.10, 1.1.1 and 1.2.1. Fixed releases of the main products embedding it: Node.js 22.23.4, 24.22.1 and 26.12.1 (end-of-life lines 20.x and older and 25.x receive no fix), Bun 1.4.4, Envoy 1.37.8, 1.38.6, 1.39.3 and 1.40.0, Istio 1.29.9, 1.30.6 and 1.31.2, Python Brotli 1.2.1 and brotlicffi 1.2.1.0. Products that link against the system library depend on the Brotli package of the Linux distribution. Recommendations Update every component that embeds the Brotli decoder (only real fix). Start with the assets flagged by this control. Restart the processes after the update. Rebuild containers, single-executable applications and appliances that bundle an affected runtime or library. Reduce the exposure until the update is deployed. Reject requests with "Content-Encoding: br" at the reverse proxy, load balancer or WAF, case-insensitively and including lists such as "gzip, br". On Envoy and Istio, disable request decompression for Brotli. Contact your edge provider about the status of the pathing (Fastly / Plateform.sh) Review outbound calls. List the features that fetch content from servers you do not control, and patch the services that host them first.