CVE-2026-1801C (QUANTUM-SHIFT) / CVE-2026-180A7 (BAL-JUMP): Static Analysis of Movement Input Heuristics in Source 2 (server.dll)

Abstract

This paper presents a static reverse-engineering analysis of two client-side movement verification routines implemented in the Counter-Strike 2 engine (server.dll): the input automation / SOCD evaluator (sub_1801C6B30, designated CVE-2026-1801C / QUANTUM-SHIFT) and the jump request rate limiter (sub_180A7EDB0, designated CVE-2026-180A7 / BAL-JUMP). Through disassembly analysis and formal mathematical modeling of the underlying state machines, we demonstrate structural edge cases in both heuristics. Specifically, we document how discrete temporal quantization in sub_1801C6B30 creates an invariant classification boundary under fixed single-tick phase offsets, and how sub_180A7EDB0 relies on a univariant interval metric ($\Delta t$) that remains invariant under phase-locked single-impulse triggers.

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1. Input Automation Verification (sub_1801C6B30)

1.1 Routine Specification

• Target Binary: server.dll (Win64 Retail Build)
• Symbol Offset: 0x1C6B30
• Interface: void __fastcall sub_1801C6B30(int *pMovementServices, __int64 pPlayerController, __int64 pUserCmdPB)

1.2 Execution Pipeline & State Representation

The routine evaluates movement button transition events (+moveleft / +moveright) submitted via client CBaseUserCmdPB payloads. Execution follows a conditional pipeline:

1. Velocity Gating: The scalar 2D velocity magnitude squared of the player pawn must exceed a static threshold: $$|v_{xy}|^2 > (0.52 \cdot 260.0)^2 = 18279.04 \text{ unit}^2/\text{s}^2$$
2. Temporal Quantization: Transition phase deltas ($\Delta t_{\text{trans}}$) are quantized to discrete frame tick units: $$k = \text{round}\left( \frac{\Delta t_{\text{trans}}}{\tau_{\text{tick}}} \right), \quad \tau_{\text{tick}} \approx 15.625\text{ ms}$$
3. Symbolic Classification: The integer value $k \in [0, 15]$ maps to a discrete event code $c \in {1, 2, 3}$: $$c = \begin{cases} 1 & \text{if } k = 0 \text{ (Ideal 0-tick transition)} \ 2 & \text{if } k \ge 1 \text{ and state is Overlap} \ 3 & \text{if } k \ge 1 \text{ and state is Underlap} \end{cases}$$
4. Ring Buffer Storage: The classification code $c$ is stored in a circular history array of capacity $N$ (sv_auto_cstrafe_attempt_window, default 100).

1.3 Decompiled Logic (sub_1801C6B30)

void __fastcall sub_1801C6B30(int *pMovementServices, __int64 pPlayerController, __int64 pUserCmdPB)
{
    if (!pPlayerController || (*(_BYTE *)(pUserCmdPB + 16) & 1) == 0)
        return;

    __int64 pPawn = sub_180B137A0(pPlayerController);
    if (!pPawn || !(*(unsigned __int8 (__fastcall **)(__int64))(*(_QWORD *)pPawn + 3216i64))(pPawn))
        return;

    float *pVel = (float *)sub_1803CBD90(pPawn, &szVelocityBuf);
    float vSq = (pVel[0] * pVel[0]) + (pVel[1] * pVel[1]) + (pVel[2] * pVel[2]);
    
    // Gating: Minimum velocity threshold
    if (vSq <= 18279.04f)
        return;

    int rawTicks = *(_DWORD *)(pUserCmdPB + 24);
    bool bIsOverlap = (rawTicks >= 0);
    int absTicks = bIsOverlap ? rawTicks : ~rawTicks;

    double curTime = sub_1801F46D0(off_181C9F350);
    if (curTime * 1e-9 * (double)absTicks >= 15.5)
        return;

    int roundedTicks = (int)V_roundd();
    if ((unsigned int)roundedTicks > 15)
        return;

    // Symbol Assignment
    char symbolCode;
    if (roundedTicks == 0)
        symbolCode = 1; // Success / Perfect 0-tick
    else
        symbolCode = bIsOverlap ? 2 : 3; // Overlap or Underlap

    // Fetch ConVar configuration pointers
    unsigned int windowCap = *GetConVarUInt(&unk_181DDBD30, &qword_181DDBD38);
    if (windowCap - 1 > 999)
        return;

    sub_1801ECEA0(pMovementServices, windowCap);

    // Append symbol to circular buffer
    int bufCap = pMovementServices[0];
    if (bufCap > 0)
    {
        int writeIdx = pMovementServices[6];
        if (writeIdx >= 0 && writeIdx < bufCap)
        {
            *(_BYTE *)(writeIdx + *((_QWORD *)pMovementServices + 1)) = symbolCode;
            if (++pMovementServices[6] == bufCap)
                pMovementServices[6] = 0;
        }
    }

    // Update discrete tick frequency histograms
    if (bIsOverlap)
        pMovementServices[roundedTicks + 7]++;
    else
        pMovementServices[roundedTicks + 23]++;

    int seqLen = *GetConVarInt(&unk_181DDBD40, &qword_181DDBD48);
    if ((unsigned int)(seqLen - 1) > 999)
        return;

    // Evaluate sliding window sequence metrics
    int totalValid = 0;
    int totalOverlaps = 0;
    int curSequenceSuccesses = 0;
    int maxSequenceSuccesses = 0;

    for (int i = 0; i < (int)windowCap; ++i)
    {
        if (i < bufCap)
        {
            int readIdx = i + pMovementServices[6] - bufCap;
            if (i + pMovementServices[6] < bufCap)
                readIdx = i + pMovementServices[6];

            char sym = *(_BYTE *)(readIdx + *((_QWORD *)pMovementServices + 1));
            if (sym != 0)
            {
                totalValid++;
                if (sym == 2) totalOverlaps++;
                else if (sym == 1) curSequenceSuccesses++;
            }
        }

        // Sliding window update
        if (i >= seqLen && (i - seqLen) >= 0)
        {
            if ((i - seqLen) < bufCap)
            {
                int popIdx = i + pMovementServices[6] - seqLen - bufCap;
                if (i + pMovementServices[6] - seqLen < bufCap)
                    popIdx = i + pMovementServices[6] - seqLen;

                if (*(_BYTE *)(popIdx + *((_QWORD *)pMovementServices + 1)) == 1)
                    curSequenceSuccesses--;
            }
        }

        if (maxSequenceSuccesses < curSequenceSuccesses)
            maxSequenceSuccesses = curSequenceSuccesses;
    }

    int minAttempts = *GetConVarInt(&unk_181DDBD20, &qword_181DDBD28);
    float dynamicLimit = 0.0f;

    if (totalValid >= minAttempts)
    {
        int minSuccessThreshold = *GetConVarInt(&unk_181DDBD50, &qword_181DDBD58);
        if (maxSequenceSuccesses >= minSuccessThreshold)
        {
            float successRatio = 0.0f;
            if (seqLen > minSuccessThreshold)
            {
                successRatio = (float)(maxSequenceSuccesses - minSuccessThreshold) / 
                               (float)(seqLen - minSuccessThreshold);
            }

            float lowerPct = *GetConVarFloat(&unk_181DDBD70, &qword_181DDBD78); // Default 20.0%
            float upperPct = *GetConVarFloat(&unk_181DDBD60, &qword_181DDBD68); // Default 5.0%
            
            dynamicLimit = (lowerPct - upperPct) * successRatio + upperPct;
        }
    }

    float observedOverlapPct = ((float)totalOverlaps / (float)totalValid) * 100.0f;

    // Violation Condition: Dynamic limit exceeds observed overlap ratio
    if (dynamicLimit > observedOverlapPct)
    {
        sub_1801ECEA0(pMovementServices, 0); // Flush buffer state
        
        bool bEnableKick = *GetConVarByte(&unk_181DDBD90, &qword_181DDBD98);
        if (bEnableKick)
        {
            __int64 pEngine = qword_182012050;
            void (__fastcall *pfnKickClient)(__int64, unsigned int, _QWORD, __int64) = 
                *(void (__fastcall **)(__int64, unsigned int, _QWORD, __int64))(*(_QWORD *)pEngine + 768i64);

            int slotIdx = -1;
            sub_181265470(pPlayerController, &slotIdx);
            
            // Disconnect Code 162: NETWORK_DISCONNECT_KICKED_INPUTAUTOMATION
            pfnKickClient(pEngine, (unsigned int)(slotIdx - 1), 0, 162);
        }
    }
}

1.4 Mathematical Model & Classification Analysis

Let $\mathbf{S} = {s_1, s_2, \dots, s_N}$ represent the sequence of event symbols in the history buffer of size $N$. The parameter $S_{\text{max}}$ denotes the maximum number of code $1$ symbols ($s_i = 1$) within any contiguous sub-sequence of length $L$: