gosaml2 CBC Padding Panic — Unauthenticated Process Crash

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

8.7 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N · score source

EPSS

No dated EPSS signal available.

As published by the source; long descriptions are shortened.

Summary The AES-CBC decryption path in DecryptBytes() panics on crafted ciphertext whose plaintext is all zero bytes. After decryption, bytes.TrimRight(data, "\x00") empties the slice, then data[len(data)-1] panics with index out of range [-1]. There is no recover() in the library. The panic propagates through ValidateEncodedResponse and kills the goroutine (or the entire process in non-net/http servers). An attacker needs only the SP's public RSA key (published in SAML metadata) to construct the payload — no valid signature is required. Affected Version All versions of github.com/russellhaering/gosaml2 through latest (v0.9.0 and HEAD) that support AES-CBC encrypted assertions. Vulnerable Code types/encryptedassertion.go:65-79 — DecryptBytes, AES-CBC branch: Attack Details | Property | Value | |---|---| | Attack Vector | Network (unauthenticated HTTP POST to ACS endpoint) | | Authentication Required | None | | Attacker Knowledge | SP's public RSA certificate (published in SAML…

Published by the source

18 Mar 2026, 20:19 UTC

Last modified by the source

18 Mar 2026, 20:19 UTC

Source last checked

26 Oct 2026, 15:18 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-hwqm-qvj9-4jr2

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# Patch Next advisory brief: GHSA-hwqm-qvj9-4jr2

Advisory: gosaml2 CBC Padding Panic — Unauthenticated Process Crash
IDs: GHSA-hwqm-qvj9-4jr2
Record: https://patchnext.com/advisories/ghsa-hwqm-qvj9-4jr2 (revision 1, source checked 26 Oct 2026, 15:18 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/russellhaering/gosaml2 0.11.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/russellhaering/gosaml2: affected <= 0.10.0; fixed in 0.11.0

## Suggested inspection (read-only)
- Go github.com/russellhaering/gosaml2: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/russellhaering/gosaml2.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-hwqm-qvj9-4jr2 (GitHub-reviewed advisory GHSA-hwqm-qvj9-4jr2 lists affected ranges: Go github.com/russellhaering/gosaml2 >=0 <=0.10.0)

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