AIKIDO-2026-730961
phpseclib/phpseclib is vulnerable to Observable Timing Discrepancy
63
Medium Risk
This Affects:
phpseclib/phpseclibTL;DR
The pure-PHP implementation of X25519 scalar multiplication is not constant time. Field addition and subtraction perform data-dependent conditional modular reduction, so each Montgomery-ladder step takes time that depends on bits of the secret scalar. An observer able to measure per-step timing or libgmp call counts can recover the full X25519 private key, even using the standard base point and without chosen inputs. The fix blinds the Montgomery multiplication and adds constant-time handling so execution time no longer depends on private scalar bits.
Who does this affect?
You are affected if you are using a version that falls within the vulnerable range and you perform X25519 key exchange with a private key over the pure-PHP code path.
Background info
phpseclib/phpseclib is vulnerable to Observable Timing Discrepancy in versions 3.0.0 - 3.0.56 and 4.0.0 - 4.0.0.
How to fix this
Upgrade the phpseclib/phpseclib and/or the phpseclib library to the patch version.
Links
GitHub Releases
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