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CVE-2026-1801C — Static reverse-engineering analysis of movement input heuristics in Source 2 engine, identifying structural edge cases in input automation and jump rate limiting routines. | Kitploit
Tools/GitHubGitHub/misterdengi/cve-2026-1801c
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GitHubmisterdengi/cve-2026-1801c

CVE-2026-1801C

Static reverse-engineering analysis of movement input heuristics in Source 2 engine, identifying structural edge cases in input automation and jump rate limiting routines.

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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.

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)

root@kitploit:~
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 $L$:

$$S_{\text{max}} = \max_{0 \le j \le N - L} \sum_{i=j}^{j+L-1} \mathbb{I}(s_i = 1)$$

The adaptive threshold function $T(S_{\text{max}})$ is conditioned on $S_{\text{max}} \ge S_{\text{thresh}}$:

$$T(S_{\text{max}}) = \begin{cases} \theta_{\text{upper}} + (\theta_{\text{lower}} - \theta_{\text{upper}}) \cdot \frac{S_{\text{max}} - S_{\text{thresh}}}{L - S_{\text{thresh}}} & \text{if } S_{\text{max}} \ge S_{\text{thresh}} \ 0 & \text{if } S_{\text{max}} < S_{\text{thresh}} \end{cases}$$

Where default configuration values are defined as:

  • $L = 15$ (sv_auto_cstrafe_sequence_length)
  • $S_{\text{thresh}} = 10$ (sv_auto_cstrafe_success_threshold)
  • $\theta_{\text{lower}} = 20.0$ (sv_auto_cstrafe_lower_overlap_pct_threshold)
  • $\theta_{\text{upper}} = 5.0$ (sv_auto_cstrafe_upper_overlap_pct_threshold)

A violation is declared if and only if $T(S_{\text{max}}) > P_{\text{overlap}}$, where $P_{\text{overlap}}$ is the sample ratio of code $2$ events:

$$P_{\text{overlap}} = \frac{100}{N} \sum_{i=1}^{N} \mathbb{I}(s_i = 2)$$

Structural Invariant

For any input stream where the phase offset $\Delta t_{\text{trans}}$ is constrained such that $k = \text{round}(\Delta t_{\text{trans}} / \tau_{\text{tick}}) \ge 1$:

  1. $s_i \in {2, 3}$ for all $i$, yielding $\mathbb{I}(s_i = 1) = 0$.
  2. Consequently, $S_{\text{max}} = 0$.
  3. Since $0 < S_{\text{thresh}}$, $T(S_{\text{max}}) = 0$ holds identically.
  4. The inequality $0 > P_{\text{overlap}}$ evaluates to false for all non-negative $P_{\text{overlap}}$. The evaluation path terminating at pfnKickClient remains unexecuted.

2. Jump Rate Limiting (sub_180A7EDB0)

2.1 Routine Specification

  • Target Binary: server.dll (Win64 Retail Build)
  • Symbol Offset: 0x1A7EDB0
  • Interface: void* __fastcall sub_180A7EDB0(__int64 pMovementServices, __int64 pMoveData)

2.2 Decompiled Logic (sub_180A7EDB0)

root@kitploit:~
void *__fastcall sub_180A7EDB0(__int64 pMovementServices, __int64 pMoveData)
{
    __int64 pPawn = *(_QWORD *)(pMovementServices + 8);
    sub_180C28550(pPawn, 2i64);
    
    if (!*(_QWORD *)(pPawn + 56))
        nullsub_908(pPawn);

    // Collision hull & ground contact evaluation
    (*(void (__fastcall **)(_QWORD))(**(_QWORD **)(pPawn + 56) + 1624i64))(*(_QWORD *)(pPawn + 56));
    sub_1803CBD30(*(_QWORD *)(pPawn + 56));
    sub_1803CD4C0(*(_QWORD *)(pPawn + 56), v14);

    if (dword_181FDB358)
        --dword_181FDB358;

    // Check IN_JUMP bit (0x2) in command button mask
    if ((*(_BYTE *)(pPawn + 88) & 2) != 0 || sub_180C28550(pPawn, 2i64))
    {
        _BYTE *pPenaltyActive = (_BYTE *)(pMovementServices + 16);
        if (*pPenaltyActive)
        {
            float curTime = *((float *)off_181C9F350 + 12);
            float lastJumpTime = *(float *)(pMovementServices + 20);
            float penaltyInterval = sub_18029CE70(&unk_181FDB4D8, 0xFFFFFFFFi64); // sv_jump_spam_penalty_time

            // Interval evaluation: curTime > lastJumpTime + penaltyInterval
            if (curTime > (penaltyInterval + lastJumpTime))
            {
                if (*pPenaltyActive)
                {
                    sub_180A99DE0(pMovementServices + 16, 0xFFFFFFFFi64, 0xFFFFFFFFi64);
                    *pPenaltyActive = 0; // Clear penalty state
                }

                // Apply jump impulse
                sub_180A7F550(pMovementServices, pMoveData);

                if (!*pPenaltyActive)
                {
                    sub_180A99DE0(pPenaltyActive, 0xFFFFFFFFi64, 0xFFFFFFFFi64);
                    *pPenaltyActive = 1; // Engage penalty state
                }

                if (sub_180C28550(*(_QWORD *)(pMovementServices + 8), 2i64))
                {
                    // Store jump timestamp: lastJumpTime = curTime - frameTime
                    *(float *)(pMovementServices + 20) = *((float *)off_181C9F350 + 12) - 
                                                         *((float *)off_181C9F350 + 13);
                }
                return pMovementServices;
            }
        }

        bool bDebugSpam = *GetConVarByte(&unk_181FDB640, &qword_181FDB648);
        if (!bDebugSpam)
        {
            // Apply jump impulse when penalty debug is disabled
            sub_180A7F550(pMovementServices, pMoveData);
            if (!*pPenaltyActive)
            {
                sub_180A99DE0(pPenaltyActive, 0xFFFFFFFFi64, 0xFFFFFFFFi64);
                *pPenaltyActive = 1;
            }
            *(float *)(pMovementServices + 20) = *((float *)off_181C9F350 + 12) - 
                                                 *((float *)off_181C9F350 + 13);
        }
    }
    return pMovementServices;
}

2.3 Timing Model & Interval Evaluation

Let $t_n$ denote the execution timestamp of the $n$-th jump request, and $\tau_{\text{penalty}}$ denote the value of sv_jump_spam_penalty_time (typically $1$ tick, or $\approx 15.625\text{ ms}$). The state transition for penalty flag $P \in {0, 1}$ and impulse activation $I \in {0, 1}$ is defined by:

$$I_n = \begin{cases} 1 & \text{if } P_{n-1} = 0 \text{ or } t_n - t_{n-1} > \tau_{\text{penalty}} \ 0 & \text{if } P_{n-1} = 1 \text{ and } t_n - t_{n-1} \le \tau_{\text{penalty}} \end{cases}$$

Analysis of High-Frequency vs. Ground-State Locked Inputs

  1. High-Frequency Input Streams: Discrete input streams generated across consecutive frames yield intervals $t_n - t_{n-1} \approx \tau_{\text{tick}} \le \tau_{\text{penalty}}$. Under this condition, $I_n = 0$, suppressing vertical impulse generation.
  2. Ground-State Phase Locking: If a jump command is issued exclusively upon state transition to FL_ONGROUND ($P_{\text{ground}} = 1$), the inter-request duration corresponds to the ballistic flight duration $T_{\text{flight}}$:

$$t_n - t_{n-1} = T_{\text{flight}} \ge \frac{2 \cdot v_z}{g} \approx 300\text{--}500\text{ ms}$$

Because $T_{\text{flight}} \gg \tau_{\text{penalty}}$, the predicate $t_n - t_{n-1} > \tau_{\text{penalty}}$ holds unconditionally for all $n$, preventing activation of the suppression path.

3. Structural Remediation Summary

ComponentTarget SymbolCurrent PrimitiveAnalytical WeaknessProposed Remediation
Input Automationsub_1801C6B30Binary classification ($k=0$ vs $k \ge 1$) + thresholdingFixed phase offset ($k=1$) yields $S_{\text{max}} = 0$ identicallyEvaluate sample variance $\sigma^2(\Delta t)$ across all $k$; flag low-variance distributions regardless of bin index
Jump Rate Limitingsub_180A7EDB0Scalar time delta comparison ($t_n - t_{n-1} > \tau$)Invariant under airborne phase delays ($T_{\text{flight}} \gg \tau$)Evaluate velocity vector continuity and ground contact duration ($\Delta t_{\text{contact}}$)
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